Based upon a total of 50 patients with alloplastic heart valve substitute an attempt was made to verify postoperative retrogression of the signs of hypertrophy in the ECG and to correlate them with the clinical findings. In accordance with the pertaining literature, the essential criterion for assessing left hypertrophy is the Sokolow index. In corrected aortic lesions there is a close relation between retrogression of electrocardiographic signs of hypertrophy and the clinical degree of severity. All patients with a retrogressive tendency of the signs of hypertrophy showed definite improvement of clinical findings. Patients in whom the ECG deteriorated did not have good clinical findings either. This clear relationship is not demonstrable in mitral lesions, since mitral stenosis and mitral insufficiency influence the left ventricle, the left atrium and the pulmonary circulation in various ways. A discussion of the assessment of the individual ECG symptoms and their causes is added.