A form of cardiomyopathy (disease of theheart muscle) involving enlargement and thickening of the heartmuscle.

In this condition, heart muscle becomes too thick to function properly. The thickening affects the individual heart muscle cells (myocytes) and may be so severe that it interferes with the proper pumping of blood out of the heart. Sometimes there is even a partial blockage or obstruction of blood flow out of the heart. This obstruction adds to the work of the heart and may lead to fainting spells.

In HCM, myocytes also become tangled and jumbled up instead of maintaining their normal pattern. One consequence of the disarray of the myocytes is that the electrical impulses that normally run though the heart muscle cannot proceed normally, which can lead to abnormal heart rhythms (arrhythmias).

Hypertrophic cardiomyopathy is usually a familial disorder, the consequence of several defects in the genes controlling heart muscle growth. The hypertrophy of HCM usually occurs during periods of a person's rapid general growth, typically during adolescence. Younger people are likely to have a more severe form of the disease, but HCM may be diagnosed in people of all ages. HCM among people over 60 years of age is often associated with mild hypertension (high blood pressure).

The prevalence of HCM in the general population is 0.2% - 0.5%, or 2 - 5 out of 1000 people.