The results of studies of the function of the heart in 592 patients with hypertensive disease are reported. In 120 cases it was established that a dependence exists between the cardiac pains and the level of the diastolic arterial pressure, minute volume and the mass of the left ventricle (r = +0.822; p less than 0.01). The study of the magnitude of intramyocardial "stress" in 127 patients enabled the authors to distinguish those with "adequate" and "inadequate" hypertrophy. With submaximum exercise an inverse correlation (r = -0.78, p less than 0.01) was found to exist between the changes in the output fractions and the mass of the myocardium of the left ventricle, pointing to the latent cardiac insufficiency in patients with marked myocardial hypertrophy. Observation of 106 patients for 3-5 years has revealed hypertrophy involution in 20 out of 79 patients with the labile and in 2 out of 27 cases with a stable form of hypertension. A relationship was found to exist between the increase of the hypertrophy and the increase of the systolic arterial pressure, and between its decrease and the drop in the general peripheral resistance.