Summary The first twenty-eight patients with ventricular septal defect proved by cardiac catheterization have been summarized. The patients were children, with no special selection other than the diagnosis made clinically. The lesion usually was associated with electrocardiographic and roentgenologic abnormalities and with significantly elevated pressures in the right ventricle and pulmonary artery. We consider ventricular septal defect an abnormality which is serious enough in most instances to justify surgical repair with the least possible delay. Of twenty-eight patients sixteen have had surgery with fourteen successful repairs.