The normal age-related growth of the heart after the early postnatal period does not involve cell division of the cardiac muscle cell but is achieved by an increase in cell size. This age-related growth is dependent on the presence of growth hormone and thyroxine and ceases in hypophysectomized animals [2]. Adaptive or compensatory cardiac hypertrophy, conversely, can be defined as the increase in heart size occurring in response to a physiological or pathological increase in the work-load of the heart. This compensatory growth may be generalized or may involve one chamber only, depending on the cause; but physical exercise, for example, induces adaptive cardiac hypertrophy even in hypophysectomized