Several modifications of the Fontan principle are currently applied to the treatment of tricuspid atresia with low mortality. The use of these modifications in other malformations has most frequently been associated with less satisfactory results. At our institution, from June 1977 to October 1986, 35 consecutive patients, whose ages ranged from 8 months to 20 years (median age 3.4 years), underwent a modified Fontan procedure. Twenty patients with a median age of 3.2 years (group I) having tricuspid atresia (16 patients) or hypoplastic right heart syndrome (four patients) were treated by means of a right atrium-pulmonary artery anastomosis (12 patients) or right atrium-subpulmonary chamber connection (eight patients). Fifteen patients (group II) with a median age of 3.6 years, having a single left ventricle (10 patients), left atrioventricular valve hypoplasia or atresia (three patients), or double-outlet right ventricle (two patients), underwent right atrium-pulmonary artery anastomosis, together with a repositioning of the atrial septum to the right of the right atrioventricular valve, which thus left intact the inlet to the ventricle(s). The operative mortality rate was 25% in group I and 0% in group II. One patient in group I and one in group II died late postoperatively. All the 28 survivors are free of symptoms 3 months to 9 years after correction. According to our results, low risk can be associated with modified Fontan procedures in the treatment of complex heart malformations other than tricuspid or pulmonary atresia. Preserving the integrity of the entire inlet to the ventricle(s) by repositioning the interatrial septum, as done in group II malformations, might be helpful in improving the quality of the repair.