What Is Hypertrophic Cardiomyopathy?

Two people can be given exactly the same diagnosis and have hearts that misbehave in quite different ways. Hypertrophic cardiomyopathy — HCM for short — is a condition in which the heart muscle grows thicker than it should, and what that thickening actually does depends on where it settles and how much room it takes up. The short video at the top of this page, "Hypertrophic Cardiomyopathy" (about a minute and a half), puts the basics plainly: heart muscle cells enlarge and cause the walls of the ventricles — usually the left ventricle, the heart's main pumping chamber — to thicken, even though the size of the ventricle itself often stays normal. It is, the video notes, a very common condition that can affect people of any age, and men and women equally. Comparing its two main forms is the easiest way to understand what it can mean for you.

Same thickening, two different problems

In the obstructive form, the thickened muscle gets in the way. The wall between the left and right sides of the heart — the septum — may thicken and bulge into the left ventricle, narrowing the path blood takes as it leaves the heart. The ventricle then has to work harder to pump blood out, and the thickening can also disturb the nearby mitral valve, causing blood to leak backwards through it instead of moving forwards. In the non-obstructive form, nothing is physically blocking the exit — but the problem has not gone away, it has simply changed shape. The thickened muscle makes the inside of the left ventricle smaller, so the chamber holds less blood with each beat, and the walls may stiffen, so the ventricle relaxes and fills less easily between beats. Sometimes the thickening involves the whole ventricle, sometimes only its lower part, and the right ventricle can be affected too. Either way, the heart is moving less blood than the body is asking for — a strain that, over time, connects to the picture described in our guide to heart failure.

What it can feel like — and what it can feel like instead

Here the comparison flips again. Some people with HCM notice nothing at all for years, and the condition is picked up almost by accident. Others get clear signals, and the video lists the classic ones: chest pain, dizziness, shortness of breath, or fainting. Breathlessness that arrives with exertion and chest discomfort that comes and goes are the sorts of symptoms people most often describe. HCM is also known, as the video explains, as a common cause of sudden cardiac arrest in young people, including young athletes — which is why fainting, in particular, should never be shrugged off in someone young and otherwise fit, and why any of these symptoms deserve a proper cardiac assessment rather than a wait-and-see. A disturbed heart rhythm can be part of the picture too; our explainer on atrial fibrillation covers one rhythm problem cardiologists watch for in thickened hearts.

How doctors tell the two forms apart

You can't distinguish obstructive from non-obstructive HCM from symptoms alone — the forms overlap too much. The workhorse test is an ultrasound scan of the heart, which measures the thickness of the walls directly and watches whether blood flow out of the left ventricle is being obstructed as the heart beats; our guide to what an echocardiogram shows walks through what that scan involves. A tracing of the heart's electrical activity is usually part of the assessment as well — see what an ECG shows — and because HCM can run in families, your cardiologist may also ask about close relatives and whether screening them makes sense. Those conversations, and the scan results, are what shape everything that follows.

Treatment follows the form, not just the diagnosis

Because the two forms cause trouble differently, they are not managed identically. Many people — particularly with the non-obstructive form and few symptoms — need monitoring more than intervention: regular follow-up, scans to watch the thickness and filling, and a plan for the symptoms and rhythm issues that can develop. Where the obstructive form is causing significant symptoms despite medicines, procedures that reduce the thickened septum enter the discussion. The second video on this page, "Surgical Procedure for Hypertrophic Cardiomyopathy (HCM)", describes one of them — alcohol septal ablation, a catheter-based, minimally invasive treatment performed by an interventional cardiologist, offered to severely symptomatic patients who meet strict clinical criteria. Surgery to remove part of the thickened muscle is the other established route for suitable candidates. Which, if any, of these fits you is a specialist decision made on your scans, your symptoms, and your overall health — not something any article can or should call.

References & further reading

MedlinePlus — Hypertrophic cardiomyopathy (Medical Encyclopedia): https://medlineplus.gov/ency/article/000192.htm

MedlinePlus — Cardiomyopathy: https://medlineplus.gov/cardiomyopathy.html

NHLBI — Cardiomyopathy: https://www.nhlbi.nih.gov/health/cardiomyopathy

MedlinePlus — Heart Diseases: https://medlineplus.gov/heartdiseases.html

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Frequently Asked Questions

What does "hypertrophic" mean in hypertrophic cardiomyopathy?

It simply means enlarged or thickened. In HCM, heart muscle cells enlarge and the walls of the ventricles — usually the left ventricle — thicken, even though the overall size of the ventricle often remains normal.

What is the difference between obstructive and non-obstructive HCM?

In obstructive HCM, the thickened septum bulges into the left ventricle and blocks or narrows the path of blood leaving the heart, and it can make the mitral valve leak. In non-obstructive HCM there is no blockage, but the thickened, stiffened muscle leaves the chamber smaller and less able to relax and fill, so it still holds and moves less blood.

What symptoms should prompt a check-up?

The symptoms the video at the top of this page lists are chest pain, dizziness, shortness of breath, and fainting. Fainting in particular — especially in a young, fit person — should always be assessed promptly, because HCM is a common cause of sudden cardiac arrest in young people, including athletes.

How is HCM diagnosed?

The central test is an echocardiogram, an ultrasound scan that measures the wall thickness and shows whether blood flow out of the heart is obstructed. An ECG tracing and a family history are also usually part of the assessment.

Does everyone with HCM need a procedure?

No. Many people are managed with follow-up, monitoring, and medicines for symptoms. Procedures such as alcohol septal ablation, described in the second video on this page, are reserved for severely symptomatic patients — typically with the obstructive form — who meet strict clinical criteria set by their specialist team.

This article is for general education only and is not medical advice. It does not replace consultation with a qualified clinician. Chest pain, breathlessness, dizziness, or fainting should be assessed promptly by a medical professional.

Dr. Mohamed Ibrahim, MD, PhD

Physician-scientist · Founder, MedicalVideos.com

Dr. Ibrahim founded MedicalVideos.com in 2007 to make medical and surgical education freely accessible to students, clinicians, and patients.

Last reviewed: 11/11/26