Twenty-one patients with a double inlet left ventricle underwent a modified Fontan between May 1979 and August 1987. All but the first patient in this series were operated upon after August 1984. Their age at operation ranged from 4 to 23 years with a median age of 8 years. Initial palliation was required in 12 patients and the mean interval to repair was 77.1 months, ranging from 38 to 112. Only one of the criteria of Choussat was exceeded in 12 patients. The pulmonary vascular resistance was always less than 4 Um2. A direct atriopulmonary anastomosis was performed in 19 patients and an aortic homograft interposition was used in 2. There was one hospital death due to acute cardiac failure and no late deaths. The average of the mean right and left atrial pressures measured early postoperatively was 12.9 and 8 mmHg respectively. A prolonged hospitalization with a mean of 23 days, ranging from 9 to 69, was required because of recurrent pleural and pericardial effusions which usually resolved after the first 6 postoperative months. The need for early anticoagulation is recommended to prevent the risk of pulmonary thromboembolism observed in 2 of our patients. Cardiac catheterization performed in 19 patients within 1 year after surgery showed that the average of the mean right atrial pressure had decreased to 11.3 mmHg without a gradient across the anastomosis in any case. Two patients required reoperation: one for enlargement of a restrictive ventricular septal defect and the other for closure of a recurrent dehiscence of the patch used for closure of the right a-v valve. Three patients developed a significant subaortic obstruction and have been scheduled for reoperation. Ventricular function was assessed at a mean interval of 11.9 months (17 patients) and 25.5 months (13 patients) from surgery. Gated equilibrium radionuclide ventriculography showed that the ejection fraction was normal (greater than or equal to 50%) and it had increased with time in 10. Yet, the response to exercise was normal in only 5 of the 13 patients re-evaluated. Treadmill exercise testing showed an increase in exercise tolerance from a mean of 7.4 min to a mean of 8.7 min.(ABSTRACT TRUNCATED AT 400 WORDS)