A Research Guide for
HCM

An echocardiogram (heart ultrasound) measures wall thickness, looks for the obstruction pattern (SAM and mitral regurgitation), and estimates the gradient (the pressure jump across the obstruction). The general threshold for HCM diagnosis is a wall thickness of 15 mm or more in any part of the left ventricle — or 13 mm or more if you have a family history or a positive gene test.

Provocation matters. If your resting gradient is below 30 mmHg, your sonographer should perform provocation: Valsalva (bearing down), standing, or ideally an exercise echo on a treadmill or bike. Without this, latent obstruction is missed in about one-third of obstructive patients.

A cardiac MRI gives more accurate wall thickness measurements than echo (the apex is hard to image with ultrasound) and shows scar tissue (called late gadolinium enhancement, or LGE). The amount of LGE is one of the strongest predictors of long-term outcomes — especially the risk of sudden cardiac death.

CMR also helps identify the apical variant of HCM, finds dangerous structures like apical aneurysms, and helps distinguish HCM from phenocopies (Fabry disease has a distinctive imaging signal; amyloidosis has another).

If you have not had a cardiac MRI as part of your HCM workup, ask for one.

A 24- to 48-hour Holter (or longer-term event monitor) records every heartbeat looking for non-sustained ventricular tachycardia (NSVT), atrial fibrillation, and other arrhythmias. NSVT — a short run of fast beats from the ventricle — is one of the standard risk factors used to decide whether you might benefit from an implanted defibrillator.

Patients with obstructive HCM can have an abnormal blood pressure response to exercise: instead of rising as expected, the blood pressure plateaus or drops. This is another piece of the sudden death risk puzzle and helps clarify exercise tolerance and any latent obstruction.

Modern sarcomeric gene panels test 8 or more genes known to cause HCM. The yield is 30–60% in clinical HCM and is higher when there is a strong family history. A pathogenic variant in you allows cascade screening of relatives by gene test alone — far cheaper and clearer than serial echocardiograms for everyone.

You should be offered genetic counseling either before or after testing. Counseling helps explain what a positive, negative, or "variant of uncertain significance" (VUS) result means — and what it doesn't mean.

A negative gene test does not rule out HCM. About 30–60% of clinical HCM has no identifiable mutation with current technology.

• Fabry disease: Alpha-galactosidase A activity (in males) and/or GLA gene testing. Especially important if the LVH is symmetric, late-onset, or accompanied by kidney problems, neuropathy, or angiokeratomas.
• Cardiac amyloidosis: Bone scintigraphy (technetium pyrophosphate scan) for ATTR, and serum free light chains plus serum/urine immunofixation for AL. Particularly important in older adults, those with low-voltage ECG, or features like carpal tunnel syndrome history.
• Iron studies and TSH to exclude iron overload and thyroid dysfunction.

• What is my exact maximum wall thickness, and where in the heart is it?
• What is my LVOT gradient at rest, with Valsalva, and with exercise?
• Have I had a cardiac MRI? What is my percentage of LGE? Do I have an apical aneurysm?
• Was I tested for Fabry disease (alpha-galactosidase) and cardiac amyloidosis?
• Have I had a Holter or longer-term monitor? Was NSVT detected?
• Did my blood pressure rise normally during exercise testing?
• Have I been referred for genetic counseling and testing? If positive, what is my variant?
• Has my full evaluation been reviewed by an HCM specialist or specialized center?

For the first time, there are drugs designed for the actual molecular cause of HCM. The sarcomere in HCM works too hard — the heart muscle squeezes with too much force. Cardiac myosin inhibitors quiet that hypercontractility by reducing the number of actin-myosin cross-bridges that form during each heartbeat.

Mavacamten (brand name Camzyos). FDA approved in April 2022. Dosed at 5–15 mg once daily. In the pivotal EXPLORER-HCM trial, mavacamten dramatically improved exercise capacity, lowered the LVOT gradient, and improved symptoms. In VALOR-HCM, the majority of patients who were heading for septal reduction surgery were able to avoid it. About 65% of obstructive patients have meaningful gradient reduction.

Mavacamten has a REMS (Risk Evaluation and Mitigation Strategy) program in the US. This means you and your pharmacy and your prescriber are all enrolled in a monitoring program. You need a baseline echocardiogram, then a repeat echo before every dose change — usually at weeks 4, 8, and 12, then every 12 weeks long-term. If your ejection fraction (EF) drops below 50%, the dose is held until it recovers.

Aficamten (brand name Myqorzo). FDA approved December 19, 2025. Dosed at 5–20 mg once daily. In the SEQUOIA-HCM trial, aficamten showed similar gradient reduction and symptom improvement to mavacamten. It has a shorter half-life (about 3 days vs. about 7 days for mavacamten), which means more predictable onset and recovery. Like mavacamten, aficamten has a REMS program and a boxed warning for heart failure due to systolic dysfunction. Echocardiographic LVEF monitoring is required before and during treatment.

Drug interactions matter. The two drugs are processed by different liver enzymes — mavacamten mainly by CYP2C19 and CYP3A4, and aficamten mainly by CYP2C9. Many common medications — including some antifungals (fluconazole, voriconazole), the antibiotic rifampin, an antidepressant (fluvoxamine), the heart-rhythm drug amiodarone, and acid-reducers — can change the drug levels and raise the risk of heart failure. Always tell your prescriber about every medication and supplement before starting, and whenever anything changes.

Pregnancy. Both mavacamten and aficamten are contraindicated in pregnancy because of fetal risk. If you are of reproductive age, effective contraception is required during therapy, and pregnancy planning needs to be discussed in advance with both your cardiologist and an obstetrician.

Beta-blockers are usually the first medicine started. They slow the heart, allow it to fill better between beats, reduce the gradient, and ease symptoms. The non-vasodilating beta-blockers are preferred: metoprolol (especially metoprolol tartrate or succinate), atenolol, nadolol, or propranolol. Doses are often pushed higher than typical to be effective.

Non-dihydropyridine calcium channel blockers — verapamil or diltiazem — are used if beta-blockers cannot be tolerated or aren't enough. They are particularly helpful for diastolic dysfunction (stiff filling).

Disopyramide is a Class I antiarrhythmic drug with a strong "negative inotropic" effect — meaning it weakens contraction enough to reduce the gradient. It is usually added to a beta-blocker if obstruction persists. It can cause dry mouth, urinary retention, and constipation, so it is used less often now that myosin inhibitors are available.

Several medicines that are routinely used for other heart conditions can make obstructive HCM dangerously worse. Make sure every clinician who prescribes for you knows you have HCM.

• Vasodilators — nifedipine and other dihydropyridine calcium channel blockers, ACE inhibitors and ARBs (when prescribed solely to lower blood pressure), hydralazine, and most other blood-pressure-lowering vasodilators. They drop the resistance the heart pumps against, which worsens the obstruction.
• Digoxin — increases the force of contraction, which is the opposite of what obstructive HCM needs.
• IV inotropes — dobutamine and milrinone. These are sometimes given in hospital settings; in obstructive HCM they can cause severe collapse.
• Aggressive diuretics in someone who is already dry — can lower preload too much and worsen obstruction.
• PDE-5 inhibitors (sildenafil, tadalafil) — can worsen obstruction in some patients with significant gradients.

For patients with severe obstructive symptoms (NYHA class III or IV) despite optimal medical therapy, including a trial of myosin inhibitor when appropriate, the next step is septal reduction therapy (SRT).

Surgical septal myectomy (the Morrow procedure) is the gold standard at experienced centers. The surgeon opens the chest, opens the aorta, and shaves out the bulging septal muscle, often combined with mitral valve repair if needed. At high-volume HCM surgical centers, the mortality is under 1% and gradient relief exceeds 90%, with durable symptom improvement over decades.

Alcohol septal ablation (ASA) is a percutaneous (catheter-based) procedure. A small amount of pure alcohol is injected into the small artery feeding the offending septal muscle, causing a controlled, localized heart attack that thins the septum over weeks. ASA is appropriate for patients who are too high-risk for surgery, have suitable coronary anatomy, or strongly prefer a non-surgical option. The main downside is a 10–20% rate of needing a permanent pacemaker (vs. about 2% with myectomy) and somewhat higher rates of needing a repeat procedure.

The single most important predictor of a good outcome is operator and center volume. If a SRT is recommended, ask how many your operator and center do per year. The best centers do dozens to hundreds annually.

An implantable cardioverter-defibrillator (ICD) is a small device placed under the skin that monitors the heart rhythm and delivers a shock if a life-threatening rhythm is detected. Modern ICDs come in two forms: transvenous (leads run through veins into the heart) and subcutaneous (the lead stays under the skin without entering the heart — appealing for young patients).

Not every HCM patient needs an ICD. Risk is estimated using a model that combines multiple factors: maximum wall thickness (especially ≥30 mm), family history of sudden death, history of unexplained fainting, runs of NSVT, abnormal blood pressure response to exercise, extensive LGE on MRI (≥15% of LV mass), apical aneurysm, and reduced ejection fraction (EF <50%). The 2024 AHA/ACC HCM Guideline integrates these into an enhanced risk model.

The decision is a shared one. The benefit of an ICD — preventing a sudden cardiac death — has to be weighed against device-related risks (infection, lead problems, inappropriate shocks) and the lifelong presence of a device, especially in young patients.

Treatment options for non-obstructive HCM (nHCM) are currently more limited. There is no FDA-approved disease-specific therapy yet for non-obstructive disease. Myosin inhibitors have been tested here with mixed results: the ODYSSEY-HCM trial of mavacamten in non-obstructive HCM did not meet its main goals (reported in 2025), while the ACACIA-HCM trial of aficamten in non-obstructive HCM is still ongoing. Current management focuses on symptom control (beta-blockers, calcium channel blockers, diuretics if there is heart failure), arrhythmia management, ICD when indicated, and aggressive screening for and treatment of atrial fibrillation. If you have non-obstructive HCM, ask whether you are eligible for a clinical trial.

Atrial fibrillation (AF) is common in HCM (up to 25% lifetime risk) and not well tolerated — the loss of the "atrial kick" makes a stiff HCM heart fill even worse, and symptoms can deteriorate quickly. AF in HCM also dramatically increases stroke risk; most guidelines now recommend anticoagulation for any AF in HCM regardless of the usual stroke risk score.

Rhythm control (keeping you in normal rhythm with medication like amiodarone or with catheter ablation) is preferred when possible. Catheter ablation is effective in HCM but may require more than one procedure.

• Am I a candidate for mavacamten or aficamten? If so, which one would you recommend for me and why?
• What LVEF monitoring will I need on a myosin inhibitor, and how often?
• Are any of my current medications a problem — either as worsening my HCM or as a drug interaction with a myosin inhibitor?
• If medications don't control my symptoms, would I be a better candidate for surgical myectomy or alcohol ablation, and where would you send me?
• Where does my SCD risk fall — low, intermediate, or high — and is an ICD recommended for me?
• If an ICD is recommended, would a transvenous or subcutaneous device be best for me?
• If I have atrial fibrillation, what's my anticoagulation plan?
• How will we follow my disease over time — what tests, how often?

The 2024 AHA/ACC HCM Guidelines and the ACC Expert Consensus on Athletes with Cardiovascular Disease now recommend an individualized assessment of exercise risk rather than blanket disqualification. Many HCM patients — especially those who are stable, low-risk by current models, and well-managed — can safely walk briskly, hike, cycle, swim, lift moderate weights, and play recreational sports.

The factors that argue for more caution include: high SCD risk by the enhanced model, large LGE burden on MRI, significant LVOT obstruction not controlled by medication, prior cardiac arrest or sustained ventricular arrhythmia, exercise-induced symptoms (chest pain, severe shortness of breath, near-syncope), apical aneurysm, or reduced ejection fraction.

Avoid: sudden bursts of maximal exertion (sprinting, all-out powerlifting), exercise while severely dehydrated or hot, exercise after a heavy meal, and any activity that has previously triggered symptoms. Stay hydrated. Warm up gradually. Stop and rest if you feel lightheaded.

If you are an athlete, the decision about continued competitive sport should be made jointly with your cardiologist (ideally one with HCM expertise) and you, with full understanding of residual risk and the value of an ICD if one is indicated.

HCM is autosomal dominant: each first-degree relative (parent, sibling, child) has a 50% chance of carrying the same gene change. Cascade screening is the process of testing those relatives systematically.

• If a pathogenic variant has been found in you, relatives can be tested for that single variant with a simple blood test. Those who carry it need echocardiographic surveillance. Those who don't are reassured and no longer require surveillance.
• If no variant is found in you (which happens in 30–60% of cases), relatives need imaging-based screening — typically an echocardiogram and ECG every 1–3 years from late childhood through adulthood, with longer intervals later in life.

A "genotype-positive, phenotype-negative" relative — meaning they have the gene change but no visible disease yet — is monitored more frequently in adolescence and early adulthood when the disease most commonly manifests.

Most women with HCM tolerate pregnancy well, but pre-conception planning is essential. Both mavacamten and aficamten are contraindicated during pregnancy and must be stopped (with appropriate washout) before conception. Other medications such as beta-blockers (especially metoprolol) and certain calcium channel blockers can usually be continued with monitoring.

You should be seen by a cardio-obstetrics team, ideally well before conception. Delivery planning is individualized but most women can deliver vaginally; cesarean is reserved for obstetric indications. The first 24–48 hours postpartum carry the highest hemodynamic shifts and are watched closely.

• Stay hydrated. Especially in summer, after exercise, or if you have GI illness. Dehydration worsens obstruction.
• Watch for "morning lightheadedness." Standing up quickly out of bed can drop preload and provoke obstruction in some patients. Slow rises help.
• Be cautious with hot tubs, saunas, and long hot showers. They vasodilate and reduce preload.
• Avoid heavy alcohol intake. It dehydrates and can trigger AF.
• Get prompt care for any infection that causes fever, vomiting, or dehydration.
• Tell every clinician you have HCM — especially anesthesiologists, dentists doing procedures with epinephrine, and ER physicians. Carry a card or wear medical ID.
• Keep a symptom diary — especially noting any episodes of fainting, near-fainting, palpitations with symptoms, or chest pain. This information helps risk stratification at each visit.

Understand the genetic dimension. Because HCM runs in families, a diagnosis in one person often raises questions and fears in others. Encourage cascade screening — it is one of the most impactful things a family can do. Early identification gives the next generation choices.

Learn the warning symptoms. Fainting (especially with exertion), near-fainting, palpitations with chest pain or lightheadedness, sudden severe breathlessness, or chest pain during exercise are red flags. Call 911 rather than driving. If a defibrillator is part of life, learn how the device works and what to do if it fires.

Support exercise, don't over-restrict. The old culture of "no activity" for HCM patients caused real harm — deconditioning, weight gain, depression. The new model is informed, moderate exercise. Be an ally for that rather than a brake on it.

Help manage medications and monitoring. Myosin inhibitors require regular echocardiograms. A shared calendar, alerts for echo appointments, and tracking dose changes is genuinely useful. So is asking about side effects: unexplained fatigue, swelling, or new shortness of breath after a dose change can mean the ejection fraction has dropped and needs evaluation.

Make space for emotional processing. A new HCM diagnosis — especially in a young athlete, or in a young parent newly worried about their children — carries grief, identity loss, and anxiety. A counselor familiar with chronic cardiac illness can be invaluable. So can connecting with the HCMA community.

Know when to seek emergency care vs. routine follow-up. Emergency: fainting, sustained palpitations with severe symptoms, severe chest pain, severe sudden breathlessness, ICD shock. Urgent (24–48 hours): new persistent palpitations, new significant exercise limitation, new ankle swelling. Routine follow-up: stable symptoms, scheduled monitoring.

• What level of exercise is safe for me — specifically?
• Which family members should be screened, when, and how?
• If I want to have children, when should I see a cardio-obstetrics specialist?
• What should make me go to the ER vs. call your office vs. wait until my next visit?
• Are there support groups or peer connections you recommend?

Several biotech programs are developing gene therapies for HCM, particularly for patients with MYBPC3 mutations. The most prominent example, TN-201 (from Tenaya Therapeutics), uses an AAV vector to deliver a working copy of MYBPC3 to the heart. Early-phase trials are ongoing. If gene therapy proves safe and effective, it would not be a once-daily pill but potentially a one-time treatment that targets the underlying genetic cause — a fundamentally different paradigm.

Non-obstructive HCM still has no disease-specific therapy. The ODYSSEY-HCM trial of mavacamten in non-obstructive HCM did not meet its main goals (reported in 2025). The ACACIA-HCM trial of aficamten in non-obstructive HCM is ongoing; if positive, it would extend the myosin-inhibitor approach to this currently underserved population. (MAPLE-HCM, sometimes mentioned alongside these, is actually a trial in obstructive HCM comparing aficamten with metoprolol.)

Antisense oligonucleotide and siRNA approaches are in development to silence the mutant copy of sarcomeric genes while preserving the normal copy — an "allele-specific" strategy. This is still earlier-stage than gene therapy but is conceptually attractive.

Machine learning models that combine ECG signals, CMR features, genetic data, and clinical variables are being developed to improve sudden cardiac death prediction beyond current risk calculators. None is yet approved for routine clinical use, but several are in active research.

Radiofrequency septal ablation is being studied as an alternative to alcohol septal ablation, and percutaneous mitral valve interventions are being explored for SAM-related mitral regurgitation. These remain investigational.

A small minority of HCM patients (about 5–10%) progress to "burnt-out" HCM, where the thick heart muscle scars and the heart starts to dilate and pump weakly — transitioning from a hypertrophic to a dilated phenotype. Treatment here looks much more like standard heart failure management (guideline-directed medical therapy, possibly an ICD if not already in place, and evaluation for transplant or mechanical circulatory support at specialized centers).

• ClinicalTrials.gov — search "hypertrophic cardiomyopathy" with filters for your region.
• The HCMA (Hypertrophic Cardiomyopathy Association, www.4hcm.org) maintains lists of trials and can sometimes help with patient navigation.
• Specialized HCM centers — often run trials themselves or know who is enrolling. A referral to an HCM center is worth pursuing even if just for trial access.
• Ask your cardiologist directly if any trials are appropriate for your subtype (especially if you have non-obstructive HCM or apical HCM).

• Are there clinical trials that I might qualify for — for either established or experimental therapies?
• Should I be evaluated at an HCM center of excellence?
• If my disease progresses, what does the longer-term plan look like?
• How do I keep up with the latest treatments without chasing every news headline?

• Dual-chamber pacing for gradient reduction — In the 1990s, implanting a pacemaker and programming it to pre-excite the right ventricle was proposed as a way to reduce the LVOT gradient without surgery. The M-PATHY and PIC trials showed that the gradient reduction was modest and largely explained by a placebo effect. Pacing is no longer recommended as a primary treatment for obstruction, though it remains useful for conduction disease after SRT. DE-ADOPTED
• Nifedipine and other dihydropyridine calcium channel blockers — Once used broadly as vasodilators and antihypertensives, these drugs reduce afterload and worsen LVOT obstruction. They are now specifically listed as medications to avoid in obstructive HCM by both AHA/ACC and ESC guidelines. DE-ADOPTED
• Digoxin — Previously used in some HCM patients for rate control, digoxin increases myocardial contractility and worsens obstruction. It is now contraindicated in obstructive HCM. DE-ADOPTED
• Blanket competitive sport disqualification — For decades, all patients with HCM were told they could never play competitive sports. The 2024 AHA/ACC guidelines replaced this approach with individualized shared decision-making based on risk profile, allowing many stable patients to participate in moderate recreational and even some competitive exercise. DE-ADOPTED
• Prophylactic ICD for all HCM patients — Early recommendations sometimes led to broad ICD implantation. Modern risk stratification using enhanced models (including CMR-LGE quantification, apical aneurysm detection, and the ESC HCM Risk-SCD calculator) has refined patient selection. ICDs are now reserved for patients with identifiable risk factors, not implanted routinely. DE-ADOPTED
• Isoproterenol provocation testing — Previously used to provoke LVOT obstruction, isoproterenol carries significant risk of triggering dangerous arrhythmias. It has been replaced by safer methods: Valsalva, standing, and exercise echocardiography. DE-ADOPTED

• United States (FDA) — Mavacamten (Camzyos) approved April 2022 for symptomatic obstructive HCM (NYHA II–III). Aficamten (Myqorzo) approved December 2025. Both require REMS programs with echocardiographic monitoring. Genetic testing and CMR are widely available at academic centers.
• European Union (EMA) — Mavacamten received a positive CHMP opinion and was approved by the EMA in 2023 for obstructive HCM. Country-level reimbursement varies; Germany and France were among the first EU markets with access. Aficamten was approved by the European Commission in February 2026 (EU launch expected first in Germany in 2026). The ESC 2023 Cardiomyopathy Guidelines are the primary clinical framework.
• United Kingdom (NICE/MHRA) — NICE technology appraisal for mavacamten was completed in 2024, with conditional access in NHS England for patients who meet specific criteria. Aficamten NICE review is anticipated. The ESC HCM Risk-SCD calculator originated at Barts Heart Centre and is the standard UK risk stratification tool.
• Japan (PMDA) — Mavacamten was approved by the PMDA in 2024. Japan has a higher prevalence of apical HCM (the Yamaguchi variant), which accounts for 15–25% of Japanese HCM cases compared to 3–5% in Western populations. High-volume surgical myectomy programs exist at major cardiac centers.
• Canada (Health Canada) — Mavacamten received Health Canada approval in 2023. Provincial formulary listing and reimbursement timelines vary. Access to CMR and genetic testing is generally good at academic centers; wait times may be longer in some provinces.
• Australia (TGA) — Mavacamten was approved by the TGA. PBS listing discussions were ongoing as of early 2026. The Baker Heart and Diabetes Institute and Royal Melbourne Hospital are established HCM centers of expertise.

Both mavacamten and aficamten were developed and first approved in the United States, with subsequent regulatory submissions to other agencies. As of mid-2026, mavacamten has the broadest international availability (US, EU, UK, Japan, Canada, Australia, and ~50 countries in total). Aficamten, the newer agent, is approved in the US (December 2025), China (December 2025), and the European Union (February 2026), with further international approvals in progress. Septal myectomy and alcohol septal ablation are available worldwide at experienced centers. High-volume myectomy programs include Fuwai Hospital (Beijing), Bad Oeynhausen (Germany), and multiple centers in Italy. Genetic testing panels for HCM are available through international commercial laboratories, though access and reimbursement vary.

• Hypertrophic Cardiomyopathy Association (HCMA) — www.4hcm.org. The largest patient advocacy organization for HCM in the US. Educational materials, virtual and in-person support groups, clinical trial information, and patient navigators who can help you find a specialized center.
• American Heart Association (AHA) — www.heart.org. HCM-specific educational content and the local Utah chapter offers community programs.
• 4HCM Foundation — patient support resources for newly diagnosed families, with a focus on family screening awareness.
• Sudden Cardiac Arrest Association (SCAA) — useful for families of survivors and for advocacy work.

• University of Utah Health Cardiovascular Genetics Program — comprehensive genetic testing, counseling, and cascade family screening for HCM and other inherited cardiomyopathies.
• University of Utah Health Heart Failure and Cardiomyopathy Clinic — an HCMA-recognized Center of Excellence. Specialized HCM management including cardiac myosin inhibitor therapy, advanced cardiac imaging, and SCD risk assessment. Referral: (801) 585-7676.
• Intermountain Medical Center Heart Institute — Hypertrophic Cardiomyopathy Center (Murray, UT) — an HCMA National Center of Excellence, caring for adults at Intermountain Medical Center and children at Primary Children's Hospital. Advanced imaging (CMR with LGE) and comprehensive HCM management.
• University of Utah Cardiac Surgery — septal myectomy program with access to experienced operators through regional referral networks for high-volume centers when indicated.
• American Heart Association Utah chapter — cardiac rehabilitation resources, support groups, and community education events.

For complex decisions — especially septal reduction therapy, difficult diagnoses, and consideration of clinical trials — a recognized HCM center can be transformative. Importantly, Utah has two in-state HCMA Centers of Excellence — University of Utah Health and the Intermountain Medical Center Heart Institute HCM Center — so many Utahns can receive Center-of-Excellence-level care without leaving the state. Other well-established programs for the most complex or trial-specific cases include the Mayo Clinic (Rochester), Cleveland Clinic, Tufts Medical Center HCM Institute, Mount Sinai, Stanford, Duke, and Northwestern. The HCMA maintains a current list and patient navigators at www.4hcm.org (+1 973-983-7429), including Lori Fund travel grants.

• All prior imaging on disk or via portable media (echo and especially CMR images, not just the reports)
• Holter and event monitor recordings
• Genetic test reports (and any family member results)
• A current medication list with doses
• A written family history (who, when diagnosed, who died young or suddenly)
• A symptom diary — episodes, triggers, severity, recovery
• Your questions, written down

This guide is educational and is not a substitute for individualized medical advice from your cardiologist or other qualified clinicians. Decisions about HCM testing, medication, devices, surgery, exercise, pregnancy, and family screening are highly individual and should always be made through shared decision-making with a clinician who knows your specific case. Information about drugs, devices, and trials evolves rapidly; verify current recommendations with your care team.

• HCM (hypertrophic cardiomyopathy) — A genetic heart condition in which the heart muscle becomes abnormally thick, making it harder for the heart to pump blood efficiently.
• LVOT obstruction (left ventricular outflow tract obstruction) — A blockage in the path where blood exits the heart's main pumping chamber. In HCM, the thickened muscle can narrow this passage, especially during exercise or exertion.
• SAM (systolic anterior motion) — An abnormal forward movement of the mitral valve leaflet during each heartbeat that can worsen LVOT obstruction and cause the mitral valve to leak.
• Cardiac myosin inhibitor — A newer class of medication that works by reducing the force of heart muscle contraction, which helps relieve obstruction and improve symptoms in HCM.
• Mavacamten (Camzyos) — The first FDA-approved cardiac myosin inhibitor for obstructive HCM. It reduces the excessive contraction force that causes obstruction, and requires regular echocardiogram monitoring.
• Aficamten (Myqorzo) — A second-generation cardiac myosin inhibitor approved for obstructive HCM. It works similarly to mavacamten but may require less frequent monitoring.
• Septal myectomy — Open-heart surgery in which a surgeon removes a small portion of the thickened heart muscle (septum) to widen the outflow tract and relieve obstruction.
• Alcohol septal ablation — A catheter-based procedure in which a small amount of alcohol is injected into a blood vessel supplying the thickened septum, causing that portion of muscle to shrink over time and reduce obstruction.
• SCD (sudden cardiac death) — An unexpected death caused by a sudden loss of heart function, usually due to a dangerous heart rhythm. SCD risk assessment is a critical part of HCM care.
• ICD (implantable cardioverter-defibrillator) — A small device placed under the skin that continuously monitors heart rhythm and delivers an electric shock to restore a normal heartbeat if a life-threatening arrhythmia occurs.
• Cardiac MRI — A specialized imaging scan that uses magnetic fields to create detailed pictures of the heart's structure, thickness, and scarring. It is considered the gold standard for evaluating HCM.
• LGE (late gadolinium enhancement) — A technique used during cardiac MRI in which a contrast dye highlights areas of scarring (fibrosis) in the heart muscle. The amount of scarring helps predict arrhythmia risk.
• Sarcomere — The basic contractile unit inside heart muscle cells. Mutations in genes that encode sarcomere proteins are the most common cause of HCM.
• Phenocopy — A condition that mimics the appearance of HCM on imaging but is caused by a different underlying disease, such as Fabry disease or cardiac amyloidosis. Identifying phenocopies is important because their treatments differ.
• Fabry disease — A rare genetic disorder that causes fatty substances to build up in cells throughout the body, including the heart. It can cause heart wall thickening that looks like HCM but requires enzyme replacement therapy instead.
• ATTR amyloidosis (transthyretin amyloid cardiomyopathy) — A condition in which an abnormal protein called transthyretin misfolds and deposits in the heart muscle, causing it to stiffen and thicken. It is an important HCM phenocopy, especially in older adults.