Four patients with isolated hypoplasia of the right ventricle who underwent intracardiac repair are described. An atrial septal defect (ASD) was successfully closed in 3 patients with mild hypoplasia of the right ventricle. The remaining patients underwent ASD closure and right atrium-to-pulmonary artery connection with a conduit with a bovine pericardial valve because of severe hypoplasia of the right ventricle and tricuspid valve. Postoperative angiocardiogram in the last patient demonstrated two-channel pathways from the right atrium to the pulmonary artery via both the right ventricle and external conduit. At long-term follow-up studies, 3 patients had developed arrhythmias and/or sinus node dysfunction, and one had died, probably because of arrhythmia, 13 years postoperatively. The right ventricular ejection fractions were below normal levels at 11 and 12 years postoperatively in 2 patients who underwent closure of ASD. It was concluded that the mild form of hypoplasia of the right ventricle should be surgically corrected by ASD closure, while right atrium-to-pulmonary artery connection or Fontan's operation should be chosen for cases of severe hypoplasia. Arrhythmias and hypofunction of the right ventricle are long-term problems after intracardiac repair of this anomaly.