SUMMARY Diagnosis of an uncomplicated ventricular septal defect is based on the presence of a coarse systolic thrill and long, harsh systolic murmur maximal in the fourth and fifth left parasternal spaces of a non-cyanotic individual who shows evidence of left ventricular hypertrophy and prominence of the pulmonary artery without enlargement of the aorta. Cardiac catheterization affords valuable documentation of the size of the shunt, the cardiac burden, and the hemodynamic status of the pulmonary vascular bed. Angiocardiographic techniques assist in diagnosis by demonstration of a right ventricular filling defect during right heart opacification or by premature opacification of the aorta if the shunt is reversed.