hypertrophy (hīpûr´trəfē), enlargement of a tissue or organ of the body resulting from an increase in the size of its cells. Such growth accompanies an increase in the functioning of the tissue. In normal physiology the growth in size of muscles (e.g., in an athlete as a result of increased exercise) and also the enlargement of a uterus in pregnancy are caused by hypertrophy of muscle cells. In pathology the thickening of the heart muscle from overstrain, as in hypertension (high blood pressure), is the result of hypertrophy. An organ subjected to extra work (e.g., the one kidney left to function after surgical removal of the other) usually compensates by enlarging; in such cases hyperplasia, an increase in the number of cells, generally accompanies hypertrophy.

athlete's heart, common term for an enlarged heart associated with repeated strenuous exercise. As a result of the increased workload required of it, the heart will increase physiologically by enlarging chambers and muscle mass, or hypertrophy by enlarging the size of the chambers and increasing the volume of blood pumped per stroke. Consequently, the heart has to contract less frequently and at rest will beat as few as 40 times per minute as compared with an average number of 70 beats in a normal heart. The condition is not pathological, and there is generally no danger of cardiac disability arising from it.