Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality.

The presence of an abnormality of cardiac function that is responsible for the failure of the heart to pump blood at a rate that is commensurate with the needs of the tissues or a state in which abnormally elevated filling pressures are required for the heart to do so. Heart failure is frequently related to a defect in myocardial contraction.

Left ventricular outflow tract (LVOT) obstruction can occur at the valvular, subvalvular, or supravalvular level. In general, there is an obstruction to forward flow which increases afterload, and if untreated, can result in hypertrophy, dilatation, and eventual failure of the left ventricle.

Perceived difficulty to breathe that occurs with exercise or exertion and improves with rest.

The presence of excessive connective tissue in the endocardium.

Pulmonary hypertension is defined mean pulmonary artery pressure of 25mmHg or more and pulmonary capillary wedge pressure of 15mmHg or less when measured by right heart catheterisation at rest and in a supine position.

A nonparallel arrangement of cardiac myocytes.

An increase in cell size, enhanced protein synthesis, and heightened organization of the sarcomere within cardiac myocytes.

Apical hypertrophic cardiomyopathy (AHCM) is diastolic dysfunction due to abnormal stiffness of the left ventricle during diastole, with resultant impaired ventricular filling. In AHCM thickened apical segments produce a crowded, spade-shaped, small apical cavity.

An abnormally increased ejection fraction of the left ventricle, usually defined as a left ventricular ejection fraction greater than 70 percent.