Although the incidence of complete heart block and residual shunt following closure of ventricular septal defects is very low in modern series, the risk of these complications still exists. Closing the inferior margin of a perimembranous VSD in the beating heart, may in some cases, be a safe technique which eliminates the risk of atrioventricular block and residual shunt.In 17 patients operated on for isolated VSD (Group I), the inferior margin of the defect was closed in the beating heart. The results of this technique have been compared with another 158 patients (Group II) in whom the VSD was closed under cardioplegic arrest.In Group I complete atrioventricular block developed during the placing or tying down of the sutures in 2 patients (11.7%). Normal sinus rhythm returned in 2 minutes following removing and replacement. Additional sutures were placed for residual shunt in 3 patients (17.6%). Of the 158 patients in Group II, there was complete atrioventricular block in 12 (7.5%) in the early postoperative period, and 4 (2.5%) later required a permanent pacemaker. Endocarditis prophylaxis was given to 13 patients (8.2%) because of hemodynamically insignificant residual shunts. Three patients (1.9%) were reoperated for a significant shunt.Closing the inferior margin of a perimembranous VSD in the beating heart is a safe technique which eliminates the risk of atrioventricular block and residual shunt.