Pathophysiology
The ventricle in HCM shows a marked increase in myocardial mass and a diminution in ventricular cavity size. (As portrayed in this animation.) The atria are dilated and can also be enlarged. Although the individual development of the various forms of enlargements, most commonly both the septal and lateral walls are hypertrophied (enlarged)

The major systolic abnormality is the pressure gradient of the left ventricular outflow tract; the abnormal growth of the muscle will narrow the size of the outflow tract and lead to increased outflow blood velocity. Exercise will increase (worsen) the pressure gradient both during and after the exercise.

Diastolic function is reduced and will result in elevated ventricular filling pressure. Early diastolic filling is hindered and late diastolic filling is prolonged. Isovolumic relaxation time is prolonged. This may lead to regional myocardial ischemia due to reduced nutritional flow.