Seventeen patients with idiopathic hypertrophic subaortic stenosis were examined by the M-method of echocardiography with the "Ekoline 20-A" apparatus. In all patients the interventricular septum was hypertrophied asymmetrically within limits of 15-22 mm, 17 mm on the average. The ratio of the thickness of the interventricular septum and that of the left-ventricular posterior wall amounted to 1.4-1.9, 1.6 on the average. The amplitude of movements of the interventricular septum did not exceed 3 mm and the degree of its systolic thickening ranged between 0 and 28%, being 13% on the average. In 16 patients there was anomalous systolic movement of the anterior mitral cusp to the front taking up an average of 56% of the time of the left-ventricular systole. The rate of early diastolic closure of the anterior mitral cusp was diminished from 37 to 58 mm/sec. Midsystolic closure of the aortic valve coinciding with maximum systolic murmur was noted in 9 patients. The left atrium was enlarged in 5 patients, one of whom developed atrial fibrillation. Intensification of symptoms of left-ventricular obstruction in amyl nitrite inhalation and in the first postextrasystole complex was noted. Treatment with propranolol in a dose of 60-120 mg for 3 to 9 months caused no changes in the echocardiogram.