Hypertrophic cardiomyopathy is characterized by:

Hypertrophic cardiomyopathy (HCM) is primarily characterized by the abnormal thickening of the heart muscle, particularly in the left ventricle. This thickening often leads to a reduced ventricular volume because the increased muscle mass can obstruct the outflow of blood, limiting the space available within the ventricle for filling with blood during diastole. As a result, the heart's ability to accommodate blood volume is compromised, which is a hallmark of HCM.

While an enlarged left atrium can occur as a consequence of the left ventricle's inability to efficiently pump blood, it is not a defining characteristic of HCM itself. A decrease in heart rate is not typically associated with hypertrophic cardiomyopathy; in fact, patients can often have a normal to increased heart rate depending on the circumstances. An enlarged right ventricle is also not a characteristic of HCM, as the condition primarily affects the left half of the heart. Hence, the defining feature of reduced ventricular volume directly relates to the pathophysiology of hypertrophic cardiomyopathy.