Causes

Hypertrophic cardiomyopathy is usually caused by abnormal genes (gene mutations) that cause the heart muscle to grow abnormally thick.

In most people with hypertrophic cardiomyopathy, the muscular wall (septum) between the two bottom chambers of the heart (ventricles) becomes thicker than normal. As a result, the thicker wall may block blood flow out of the heart. This is called obstructive hypertrophic cardiomyopathy.

If there's no significant blocking of blood flow, the condition is called nonobstructive hypertrophic cardiomyopathy. However, the heart's main pumping chamber (left ventricle) may become stiff. This makes it hard for the heart to relax and reduces the amount of blood the ventricle can hold and send to the body with each heartbeat.

People with hypertrophic cardiomyopathy also have an abnormal arrangement of heart muscle cells (myofiber disarray). This can trigger arrhythmias in some people.