Hypertrophic Cardiomyopathy (HCM): What Patients Need to Know
Hypertrophic cardiomyopathy, almost always shortened to HCM, is the most common inherited heart condition. By the standard definition (heart muscle that is at least 15 millimeters thick on echocardiogram with no other explanation), it affects roughly one in five hundred adults. When you add in family members who carry the gene and patients picked up by more sensitive imaging, the number rises to about one in two hundred. Many of those people never know they have it, since HCM can sit completely silent until an echocardiogram done for some other reason picks up unexpectedly thick heart muscle. For other patients, HCM is the reason for unexplained shortness of breath, chest pain, fainting, or, in the most tragic cases, sudden cardiac death in a young athlete.
The last five years have transformed how cardiologists treat HCM. New medications, better imaging, refined risk tools, and updated guidelines have turned HCM from a feared diagnosis into a very manageable one for most patients. This article walks you through what HCM is, how I think about your risk, what treatments we have, and what the diagnosis means for you and your family.
What HCM Actually Is
HCM is a condition where the heart muscle, especially the wall of the left ventricle (the main pumping chamber), grows abnormally thick without any obvious cause like high blood pressure or an aortic valve problem. The diagnostic threshold is a wall thickness of 15 millimeters or more. A wall of 13 or 14 millimeters can also be diagnostic if you have a family member with HCM or carry one of the known HCM genes. Children get diagnosed using growth-adjusted thresholds rather than absolute numbers.
We confirm the diagnosis with two imaging tests: an echocardiogram (an ultrasound of the heart) and a cardiac MRI. The MRI is especially helpful because it can show areas of scar tissue inside the thickened muscle. The more scar, the higher the risk of dangerous heart rhythms.
Under a microscope, HCM has a distinctive look. The muscle fibers are bigger than normal and arranged in a disorganized pattern that pathologists call myocyte disarray. There is scar tissue between cells, and the small arteries inside the heart muscle can be thick-walled. These tiny structural changes are what drive both the mechanical problems (the heart not filling well) and the electrical problems (irregular rhythms).
The Genetics
HCM is fundamentally a problem with the sarcomere, the molecular machinery that makes heart muscle contract. Mutations in the genes that build sarcomere parts throw off the contractile machinery, and the muscle remodels itself in response, getting thicker and stiffer over years.
Two genes account for about half of inherited cases: MYH7 (which builds a part called beta-myosin heavy chain) and MYBPC3 (which builds myosin-binding protein C). A long list of other genes account for smaller fractions. HCM is inherited in an autosomal dominant pattern, which means that each child of an affected parent has a 50 percent chance of inheriting the gene.
When we send a patient with HCM for genetic testing, we find a clearly disease-causing variant in only about 30 to 40 percent of cases. That means a majority of people with HCM have no identifiable genetic cause and no obviously affected relatives. We do not yet fully understand the rest. Common variants likely act as small modifiers that add up to risk in some patients without producing a clear single-gene answer.
The Three Main Patterns
HCM is asymmetric in most patients, meaning the muscle is thickest at one specific spot. The most common spot is the upper part of the wall between the two ventricles, just below the aortic valve. When that part is thick enough, it narrows the path that blood takes when leaving the left ventricle. We call this obstructive HCM, or LVOT obstruction. The mitral valve leaflet can get pulled forward into that narrow path during each heartbeat, making the obstruction worse and causing leakage of the mitral valve.
About a third of patients have obstruction at rest. Another third develop obstruction only with provocation: standing up suddenly, straining, or exercising. The remaining third have no obstruction at all (non-obstructive HCM). This distinction matters because the two groups have different treatment options and different long-term outlooks.
Apical HCM is a less common variant where the thickening is concentrated at the bottom tip of the ventricle rather than the wall above. It is more common in patients of Japanese descent and produces a characteristic spade-shaped chamber on imaging. Obstruction is unusual with apical HCM, and the long-term outlook tends to be better. Some apical HCM patients do develop a small aneurysm at the tip of the ventricle over time, which we monitor.
Across all three patterns, one shared problem is poor relaxation of the ventricle (we call it diastolic dysfunction). The thickened, stiffened muscle does not relax properly between beats, which raises the pressure inside the ventricle when it tries to fill. That elevated pressure backs up into the left atrium, stretches it, and over years contributes to atrial fibrillation.
What Symptoms Look Like
Many patients with HCM have no symptoms at all and only learn they have it from family screening or an echocardiogram done for some unrelated reason. When symptoms do appear, they include shortness of breath with exertion, chest pain, palpitations, lightheadedness, fainting, or signs of heart failure. Atrial fibrillation is a common complication and is poorly tolerated in HCM patients, since the stiff ventricle relies on the synchronized push from the atrium to fill properly.
The reassuring truth is that for most people with HCM, the long-term course is benign. The overwhelming majority live a normal lifespan. The minority at higher risk are exactly the group we focus our most intense monitoring and treatment on.
Sudden Cardiac Death Risk
HCM is one of the better-known causes of sudden cardiac death in adolescents and young adults, which is why it gets so much attention in the news after a young athlete dies on the field. The risk is real, and it is also concentrated in a small minority of patients. Most of HCM care, and most of the guideline framework, is built around identifying which patients are at high enough risk to benefit from an implantable cardioverter defibrillator, or ICD.
The risk factors I look at include short bursts of fast irregular heart rhythm on a heart monitor (called nonsustained ventricular tachycardia), unexplained fainting, a family history of sudden cardiac death, and a wall thickness of 30 millimeters or more. The amount of scar shown on cardiac MRI matters too: scar that involves 15 percent or more of the left ventricular mass raises risk further. Apical aneurysm and reduced pumping function are additional warnings. There is also a signal from the genetic data that patients carrying a clear sarcomere mutation tend to develop the disease earlier and have more events than patients who do not.
The American and European guidelines each have a risk calculator that integrates these factors. My approach is to talk through the risk numbers openly with every HCM patient, monitor closely, and offer ICD placement when the calculated risk crosses guideline thresholds. ICDs are not for everyone with HCM. They are for the patients whose risk profile pushes them above the line.
Medications
For symptomatic obstructive HCM, medications come first.
Beta-Blockers
Beta-blockers have been the foundation of HCM therapy for more than half a century. They slow the heart rate, give the ventricle more time to fill, and reduce the obstruction. We titrate the dose up as you tolerate it, balancing benefit against any symptoms of bradycardia (a slow heart rate). The evidence base for beta-blockers in HCM rests more on physiology and decades of clinical experience than on big randomized trials, and they remain the first medication I reach for in most obstructive patients.
Calcium Channel Blockers and Disopyramide
If beta-blockers do not work or are not tolerated, the next step is usually a calcium channel blocker like verapamil. Disopyramide, an older antiarrhythmic that depresses contraction, gets added when symptoms persist on the first two options.
Mavacamten (Camzyos)
Mavacamten is the first-in-class cardiac myosin inhibitor, FDA-approved in 2022 for symptomatic obstructive HCM. It targets the molecular problem in HCM directly by reducing how aggressively the muscle fibers contract. In the EXPLORER-HCM trial, 37 percent of patients on mavacamten met the primary composite endpoint of meaningful gains in exercise capacity and symptom class, versus 17 percent on placebo. In the VALOR-HCM trial, 82 percent of patients on mavacamten avoided needing a septal reduction procedure at 16 weeks, compared with 23 percent on placebo. Those are large effect sizes for a single drug.
Mavacamten is dispensed under a Risk Evaluation and Mitigation Strategy (REMS) program in the United States. The reason: in some patients the drug pulls the ejection fraction down below 50 percent. In EXPLORER-HCM, that happened to about 5 percent of patients during the trial. In the long-term extension MAVA-LTE, it happened to roughly 9 percent at some point. In VALOR-HCM at 128 weeks, about 14 percent of patients had a transient EF dip below 50 percent. We sometimes have to pause the drug temporarily, and you need echocardiograms on a fixed schedule throughout treatment.
Aficamten (Myqorzo)
Aficamten is the next-in-class cardiac myosin inhibitor, FDA-approved in December 2025 for symptomatic obstructive HCM. It works by the same broad mechanism as mavacamten with two practical advantages: no clinically meaningful drug-drug interactions, and a gentler dose-response curve that makes it easier to titrate without overshooting. In the SEQUOIA-HCM trial, aficamten increased peak oxygen uptake during exercise by 1.7 ml/kg/min more than placebo and nearly doubled the proportion of patients whose symptom class improved by one level or more. The MAPLE-HCM trial then went head-to-head against metoprolol (a beta-blocker) and showed a 2.3 ml/kg/min advantage in exercise capacity along with bigger reductions in obstruction and left atrial size. For patients who cannot tolerate mavacamten's monitoring schedule or drug interactions, aficamten is an attractive option.
Septal Reduction Therapy
When medications do not adequately control symptoms in obstructive HCM, the next step is a procedure to physically remove or shrink the thickened part of the wall causing obstruction. We call this septal reduction therapy. There are two ways to do it.
Surgical myectomy is open-heart surgery in which the cardiac surgeon removes a portion of the thickened wall. In experienced hands at high-volume centers, the operative mortality is well under one percent, and the symptom relief is durable for decades. I refer younger patients, patients who also need mitral valve work, and patients who need coronary bypass surgery anyway to surgical myectomy.
Alcohol septal ablation is a catheter-based alternative. The cardiologist threads a catheter into a small artery branch that supplies the thickened part of the wall and injects pure alcohol, creating a controlled, contained heart attack that scars the muscle down. The big advantage is that it avoids open-heart surgery, which makes it appealing for older patients or patients with other medical problems that raise surgical risk. The trade-off is that it can damage the heart's electrical wiring and lead to needing a pacemaker.
Either procedure relieves symptoms. Neither cures the underlying genetic disease or stops it from progressing in other parts of the heart. You stay in cardiology care for life.
Exercise and Sports
For decades, patients with HCM were systematically excluded from vigorous exercise and competitive sports on the theory that exertion provokes sudden death. That blanket restriction has shifted. Newer evidence shows that tailored exercise improves your functional capacity, your quality of life, and your psychological well-being. Competitive sport has been done safely in selected low-risk patients without a clear safety signal in the data.
Current European and American guidelines support shared decision-making between you and your cardiologist about exercise. We do an exercise stress test in HCM patients regardless of symptoms to look for hidden obstruction and assess your capacity. The blanket ban has been replaced by individualized recommendations, which most of my patients find a relief.
Family Screening
Since HCM is autosomal dominant, every first-degree relative of a patient (parents, siblings, children) should be screened. The basic screening is an echocardiogram and an ECG. For relatives of patients diagnosed in childhood, we repeat screening every one to three years. For relatives of patients diagnosed as adults, every three to five years.
Genetic testing has become more available and affordable. If your family has a known disease-causing mutation, relatives who test negative for that variant can stop the repeated imaging. Relatives who test positive but do not yet show disease on imaging stay in surveillance. For families without an identified mutation, surveillance imaging continues without the genetic shortcut.
When I talk to patients about screening, I emphasize that it is straightforward and that catching HCM early gives us far more treatment options than catching it after symptoms develop.
Frequently Asked Questions
Does HCM mean I will have sudden cardiac death?
No. The great majority of people with HCM live a normal lifespan. Sudden cardiac death is concentrated in a small minority of patients with identifiable risk factors, and modern risk stratification plus ICDs in those patients have substantially reduced that risk. Most of my HCM patients are doing well on a simple medication regimen and living normal lives.
Should I stop exercising?
Almost certainly not. Tailored exercise improves quality of life and functional capacity, and modern guidelines support individualized recommendations over blanket restriction. High-intensity competitive sport is a case-by-case conversation, and most everyday activity is safe and recommended. An exercise stress test is usually part of the evaluation that informs my specific recommendations for you.
If I have HCM, should my kids be tested?
Yes. First-degree relatives should have an echocardiogram and an ECG at defined intervals. If genetic testing has identified your family's specific mutation, cascade genetic testing of relatives can sort out who needs continued imaging surveillance and who can stop. Pediatric cardiology takes the lead for screening in children.
What is the difference between HCM and athletic heart?
Trained athletes, especially endurance athletes, can develop mild physiologic thickening of the left ventricle. Athletic heart usually shows less wall thickness, a larger chamber, normal relaxation, and the changes regress when training stops. HCM shows more pronounced thickening, often asymmetric, with abnormal relaxation, and does not regress with deconditioning. Cardiac MRI, family history, and genetic testing help us tell the two apart when imaging alone is ambiguous.
Is mavacamten a cure?
No, and it is the closest we have to disease-modifying therapy for obstructive HCM. It targets the molecular problem and produces meaningful symptom relief in most patients. It does not reverse the existing scar tissue or change the underlying genetic disease, so you take it long-term. For many patients it delays or avoids the need for septal reduction surgery entirely.
Do I need an ICD just because I have HCM?
Not automatically. ICD placement is reserved for patients whose risk score crosses guideline thresholds, not for every HCM patient. The decision involves your history, your imaging, your monitor data, and your family history. Many HCM patients never need an ICD.
References
1. Ommen, Steve R., Carolyn Y. Ho, Imran M. Asif, et al. "2024 AHA/ACC/AMSSM/HRS/PACES/SCMR Guideline for the Management of Hypertrophic Cardiomyopathy." Journal of the American College of Cardiology 83, no. 23 (2024): 2324-2405.
2. Braunwald, Eugene. "Hypertrophic Cardiomyopathy." New England Journal of Medicine 392, no. 6 (2025): 553-565.
3. Marian, Ali J., and Eugene Braunwald. "Hypertrophic Cardiomyopathy: Genetics, Pathogenesis, Clinical Manifestations, Diagnosis, and Therapy." Circulation Research 121, no. 7 (2017): 749-770.
4. Olivotto, Iacopo, Artur Oreziak, Roberto Barriales-Villa, et al. "Mavacamten for Treatment of Symptomatic Obstructive Hypertrophic Cardiomyopathy (EXPLORER-HCM): A Randomised, Double-Blind, Placebo-Controlled, Phase 3 Trial." Lancet 396, no. 10253 (2020): 759-769.
5. Desai, Milind Y., Anjali Owens, Jeffrey B. Geske, et al. "Mavacamten in Patients with Hypertrophic Cardiomyopathy Referred for Septal Reduction (VALOR-HCM)." Journal of the American College of Cardiology 80, no. 2 (2022): 95-108.
6. Maron, Martin S., Ahmad Masri, Michael E. Nassif, et al. "Aficamten for Symptomatic Obstructive Hypertrophic Cardiomyopathy (SEQUOIA-HCM)." New England Journal of Medicine 390, no. 20 (2024): 1849-1861.
7. Garcia-Pavia, Pablo, Martin S. Maron, Ahmad Masri, et al. "Aficamten or Metoprolol Monotherapy for Obstructive Hypertrophic Cardiomyopathy (MAPLE-HCM)." New England Journal of Medicine 393 (2025).
8. Fatkin, Diane, Hugh Calkins, Perry Elliott, et al. "Contemporary and Future Approaches to Precision Medicine in Inherited Cardiomyopathies." Journal of the American College of Cardiology 78, no. 25 (2021): 2551-2572.
9. Camzyos (Mavacamten) and Myqorzo (Aficamten) FDA Prescribing Information.
Published on damianrasch.com. The above information was composed by Dr. Damian Rasch, drawing on individual insight and bolstered by digital research and writing assistance. The information is for educational purposes only and does not constitute medical advice.