The optimal management of patients with small aortic anulus or left ventricular outflow tract obstruction remains unclear. Between 1976 and March, 1982; 18 patients have undergone enlargement of their left ventricular outflow tract by means of the Konno or a modification of the Konno procedure. Fourteen of these 18 patients had previous operations for aortic stenosis or tunnel left ventricular outflow tract, and two patients had undergone three previous operations. All 18 patients had symptoms of either heart failure of chest pain, or had electrocardiographic evidence of strain. They ranged in age from 4 years to 58 years, with 13 of the 18 patients being less than 20 years of age. A Dacron patch was used to enlarge the left ventricular outflow tract after incising down the ventricular septum. In all patients, at least a 21 mm valve could be placed, with between 50% and 65% of the valve anulus being made up of natural tissue. The remaining portion of the valve anulus was constructed from the Dacron patch. The patch was extended up to enlarge the ascending aorta, and a pericardial patch was used to close the defect in the right ventricular outflow tract. In all 18 patients the gradient was obliterated at the time of operation. There was one early death in a patient who had previous insertion of a left ventricular apical-aortic conduit in which the heterograft valve had degenerated. There has been one late death because of bacterial endocarditis in a child who also had a parachute mitral valve and evidence of pulmonary hypertension. The remaining 16 patients are functioning well after the Konno procedure. Three are receiving warfarin sodium, and 13 are receiving aspirin. These results suggest that this is an acceptable method of treating patients with small aortic anulus or left ventricular outflow tract obstructions and would appear to have advantages over a left ventricular apical-aortic conduit.