Hypertrophic cardiomyopathy is usually caused by abnormal genes (gene mutations) that cause the heart muscle to grow abnormally thick. People with hypertrophic cardiomyopathy also have an abnormal arrangement of heart muscle cells, a condition known as myofiber disarray. This disarray can contribute to arrhythmia in some people.
The severity of hypertrophic cardiomyopathy varies widely. Most people with hypertrophic cardiomyopathy have a form of the disease in which the wall (septum) between the two bottom chambers of the heart (ventricles) becomes enlarged and obstructs blood flow. This condition is sometimes called hypertrophic cardiomyopathy with obstruction or hypertrophic obstructive cardiomyopathy. About 70 percent of people with obstructive HCM experience symptoms.
Sometimes hypertrophic cardiomyopathy occurs without significant obstruction of blood flow. However, the heart's main pumping chamber (left ventricle) may become stiff, reducing the amount of blood the ventricle can hold and the amount pumped out to the body with each heartbeat. This condition is sometimes called hypertrophic cardiomyopathy without obstruction or nonobstructive hypertrophic cardiomyopathy.
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