Ventricular mass and O2 supply of the myocardium were evaluated in patients with left ventricular hypertrophy due to stenosis or insufficiency of the aortic valve and in control patients without cardiac disease. Calculation of left ventricular mass from the angiogram was verified by autopsy data in seven patients. Total mass, O2 consumption, and coronary blood flow, each was related quantitatively to left ventricular total load (force) in all patients. Left ventricular equatorial tension, however, was greater in proportion to mass in aortic stenosis than in aortic insufficiency patients. This discrepancy could be explained by the more eccentric shape of the left ventricle in aortic stenosis. Oxygen consumption and coronary blood flow per gram of myocardium were normal at rest in patients with hypertrophy. Tachycardia induced by atrial pacing provoked myocardial lactate production in half of the patients with aortic stenosis but in none of the patients with aortic insufficiency. Surgical mortality was related to myocardial mass and lactate production.