• Congenital ventricular septal defects have been corrected in a group of 20 patients by open cardiotomy with the help of a mechanical pump-oxygenator. Direct suture was done in 3; in the other 17 a nonabsorbable sponge was sutured into the opening. Extracorporeal circulation was maintained by canulas diverting blood from the superior and inferior venae cavae to the pump and an additional cannula directing the blood from the pump into the aorta through the previously divided left subclavian artery. Four patients died during the postoperative period as a result of pulmonary complications. In most of the others the hypertension previously existing in the pulmonary system was substantially reduced, and in all there has been a pronounced improvement in general well-being. The preoperative heaving cardiac action has disappeared. Selection of candidates for this operation depends on accurate physiological studies, including cardiac catheterization. It is believed that patients with significant symptoms from ventricular septal defects associated with left-to-right shunts should have the defects closed.