Echocardiography parameters (thickness of the myocardium during the diastole, the mass of the left ventricular myocardium and its diastolic size) were compared with ECG types reflecting different combinations of signs of hypertrophy of the left ventricle (isolated increase in left ventricular voltage--type B, isolated change in the end part of the ventricular complex in the corresponding leads--type C, and combination of both signs on ECG "typical" of left ventricular hypertrophy--type D). The study was conducted on groups of patients with hypertensive disease and aorto-mitral valvular disease. Calculation of the statistically significant difference revealed an increase in the thickness of the myocardium during the diastole and in the mass of the myocardium of the left ventricle in type B and particularly in type D ECG, and a noticeable increase in the diastolic size of the left ventricle in ECG of type C and of type D in particular. This regularity confirms the conception that in increase in left ventricular voltage hypertrophy proper of the heart muscle develops in conjunction with an increase in the mass of the left ventricular myocardium mainly due to an increase in its thickness, while with changes in the end part of the ventricular complex an increase in the diastolic size of the left ventricle is revealed. The regularity is clearly detected both in hypertensive disease and in aorto-mitral valvular disease.