Ventricular septal defect is reported to be the most common congenital cardiac anomaly (1). In many cases, the presence of such a defect can be recognized on the basis of clinical findings alone. The clinical and hemodynamic changes produced by septal defects vary considerably, however, depending upon their size and location. Moreover, the diagnosis may be obscured by the presence of associated cardiac malformations. Experience with 65 cases has demonstrated that left ventricular angiocardiography is a valuable adjunct in the study of ventricular septal defects both as an aid to diagnosis and in planning treatment. Ventricular defects with left-to-right shunts in excess of 25 per cent of the systemic blood flow are readily apparent from oxygen studies obtained during right heart catheterization. Smaller shunts require more sensitive technics for their detection, such as dye dilution (2), hydrogen (3), and isotope (4) studies. With left-sided angiocardiography, both small and large defects can be consistently visualized and their location and the dynamics of the shunt determined. Preoperative information of this type can serve the clinician as a guide in patient management and can be of considerable assistance to the surgeon who undertakes the repair of the septum. Technic of Examination The success of angiocardiography in the study of ventricular septal defects depends upon the selective injection of contrast material into the left ventricle. Although other methods have been used (5–10), the most satisfactory technic in our laboratory has been retrograde arterial cath- eterization. The femoral or brachial artery is exposed and an N.I.H. side-hole catheter with a j-shaped tip is introduced through a small arteriotomy. The curved tip of the catheter is initially straightened with a semirigid metal stylet, which is kept in place until the catheter reaches the ascending aorta. When the stylet is removed, the catheter resumes its curve and is easily advanced, under fluoroscopic control, through the aortic valve into the left ventricle. A similar technic can be carried out percutaneously by the Seldinger method (11, 12). The contrast material employed in most of our cases was Ditriokon in quantities of 1 ml. per kilogram of body weight but not exceeding a total of 40 ml. in a single injection. The medium is introduced in one to two seconds with a Gidlund pressure injector. Serial biplane films are made at the rate of 6 per second for two and a half seconds. At the end of the procedure, the catheter is removed and the arteriotomy repaired with 6-0 arterial silk. The J-shaped catheter (13) has greatly facilitated this procedure. In practically every instance, the aortic valve has been crossed without difficulty, contrary to experience with a straight catheter (14). In addition, the curved tip makes it almost impossible to enter a coronary artery.