Hypertrophic cardiomyopathy is a primary myocardial disease with a wide range of clinical and morphologic characteristics. It is characterized by increased cardiac mass associated with a non-dilated, hypertrophied left ventricle. Phenotypic variability is substantial and includes both diffuse and segmental forms of left ventricular hypertrophy. Histopathologic features consist of myofiber disorganization, intramural arteriosclerosis, and pathologic fibrosis and matrix connective tissue. Associated functional derangements include dynamic obstruction to left and right ventricular outflow and diastolic dysfunction, including heart failure.