What is hypertrophic cardiomyopathy?

Hypertrophic cardiomyopathy (HCM), which is typically inherited from a parent, is a disease in which the muscle of the lower left chamber of the heart (the left ventricle) becomes abnormally thick and enlarged. This thickening typically affects some parts of the ventricle walls more than others (doctors call this “asymmetric thickening”). The most commonly affected area is the wall between the two bottom chambers known as the septum. 

HCM is a significant cause of both heart failure (for example, shortness of breath or fatigue) and sudden death. It is the most common cause of sudden cardiac death among athletes who were believed to be healthy.

Hypertrophic cardiomyopathy is a genetic disease in which the heart muscle grows abnormally, making the heart muscle thicken. The thickened heart muscle can interfere with the heart's electrical system, which increases the risk for life-threatening abnormal heartbeats (arrhythmias) and, rarely, sudden death.

Symptoms, such as shortness of breath and chest pain, may occur at any time of life. But some people never have symptoms, even though the condition may have been present for some time. In some cases, the thickened heart muscle is unable to relax between heartbeats, and the heart muscle itself does not get enough blood or oxygen, which causes chest pain. In rare cases, the thickened heart muscle becomes unable to pump enough blood to meet the body's needs, resulting in heart failure.

Hypertrophic cardiomyopathy, in contrast to the congestive type, involves an enlargement or overgrowth of the heart muscle, usually that of the left ventricle, but sometimes the right chamber is also involved. In one form of hypertrophic disease, the septum (the wall between the two ventricles) becomes enlarged and obstructs the flow of blood from the left ventricle into the aorta. The mitral valve also may be distorted by the thickened septum, leading to mitral insufficiency. The major symptoms are shortness of breath, dizziness or fainting, chest pain, and cardiac arrhythmias.

About 1 in 500 people have hypertrophic cardiomyopathy, a thickening of the muscle on the left side of the heart. Watch this video with thoracic surgeon Dr. Hiroo Takayama to learn about typical symptoms – and why certain high-risk patients may be asymptomatic.