Selection of patients and the timing of operation for closure of ventricular septal defect (VSD) can be difficult because the risk of operation must be balanced against the hemodynamic abnormality and the age and size of the infant. In the past 6 years we have individualized our approach to the timing and necessity of operation in the patient with an isolated VSD. During this period, 133 patients with VSD were evaluated, and 71 underwent operative closure of the VSD. Of the 133 patients, 90 were 2 years old or younger, and 40 of them required operation because of congestive failure and growth retardation. Of the 45 infants who did not undergo operation, 17 have small intracardiac shunts with normal pulmonary vascular resistance while the other 28 infants remain compensated and are growing despite moderate left-to-right shunts. A persistent, large intracardiac shunt was the indication for operation in 31 of the 48 older patients; the other 17 older patients remain well. Although 3 severely growth-retarded infants (2 to 4 kg) died soon after operation, all infants weighing 4 kg or more survive. No child has died during preoperative observation, and irreversible pulmonary vascular changes have not occurred. Most infants with VSD and large intracardiac shunts do require early VSD closure, but the risk of operation remains high in the tiny neonate with profound failure. With appropriate hemodynamic and clinical criteria, operation for selected infants can be delayed so that the risk of operation can be minimized.