This study deals with 341 patients who underwent operative correction of ventricular septal defect from 1954 to 1960. Seventy one patients (21%) died during operation or in the immediate postoperative period; another 30 patients (9%) died following discharge from the hospital and as late as 14 yr after operation. Postoperative cardiac catheterization was applied to 140 patients, 28 of whom were catheterized more than 5 yr after operation. Postoperative hemodynamic data were compared with available preoperative data and showed significant change in total pulmonary resistance. Although the majority of the survivors were asymptomatic, it is believed that periodic postoperative clinical and laboratory evaluation is important to the continued well being of the patient.