BACKGROUND We set out to examine the long-term results of relief of subaortic stenosis by enlargement of ventricular septal defect in patients with univentricular atrioventricular connection to a dominant left ventricle and discordant ventriculoarterial connections. METHODS Twenty-four patients underwent enlargement of ventricular septal defect between 1985 and 1998 at a median age of 3.2 years (range, 3 weeks to 14 years). Ten patients were younger than 1 year of age. Eighteen had undergone previous banding of the pulmonary trunk, 9 of whom also required repair of coarctation of the aorta. The median subaortic gradient before enlargement was 46 mm Hg. Twenty-three patients had a patch to enlarge the rudimentary right ventricle. RESULTS Five patients (21%) died in the early postoperative period. The overall survival at 1 and 3 years was 73%, and at 5 and 10 years was 68% and 60%, respectively. Complete heart block requiring insertion of a pacemaker occurred in 2 patients (8%). A Fontan operation was performed in 10 patients, 5 underwent a bidirectional Glenn procedure, and 2 required cardiac transplantation. Follow-up was complete in all survivors at a median time of 6.7 years (range, 8 months to 13 years). From the earlier part of the series, 3 patients experienced aortic insufficiency and 2 had recurrent obstruction. Factors adversely affecting survival were age younger than 1 year at operation and presence of obstruction within the aortic arch. CONCLUSIONS Our experience shows that, in patients with univentricular atrioventricular connection to a dominant left ventricle and subaortic stenosis, enlargement of the ventricular septal defect provides satisfactory relief of obstruction except in those younger than 1 year of age, and those who have associated obstruction in the aortic arch.