Hypertrophic cardiomyopathy (HCM) is a heterogeneous disorder characterized by variable degrees of left ventricular hypertrophy, normal or small left ventricular ,cavity size, and hyperdymamic systolic function.
A subset of these patients has predominantly interventricular septal hypertrophy in association with anterior motion of the mitral leaflets and subvalvular left ventricular outflow tract obstruction, a condition denoted as hypertrophic obstructive cardiomyopathy. Reports suggest that HCM is quite common, affecting 1 in 500 individuals in the general population. Both familial(autosomal dominant) and sporadic forms of this disease can occur.

In addition, there is a variant of HCM that is found in elderly, often female patients with hypertension. Prior molecular studies have determined that mutations in the genes coding for cardiomyocyte contractile proteins may be responsible for HCM. More than 50 different mutations affecting myosin heavy chains, myosin light chains, tropomyosin, and tropoins have been described thus far . Notwithstanding the wide variety of genetic abnormalities, all are associated with a common phenotype that includes cardiomyocyte hypertrophy,and interstitial fibrosis. HCM is characterized by the presence of a dynamic left ventricular outflow tract obstruction and diastolic dysfunction.

The degree of outflow obstruction is quite variable and may develop within the mid cavity of the left ventricle more commonly, below the aortic valve.

In the later presenting form, the left ventricular outflow tract is narrowed by the septal hypertrophy and, in some patients, is associated with anterior displacement of the mitral leaflets toward the interventricular septum.