Absence of the atrioventricular septum and a cleft in the anterior leaflet of the mitral valve is characteristic of almost all anomalies resulting from maldevelopment of the endocardial cushions. These changes produce a specific angiocardiographic picture, characterized in systole by a scalloped right border of the left ventricular outflow tract, with a small lucent notch within it, and in diastole by a gooseneck appearance of the subaortic portion of the ventricle. This appearance is independent of the associated hemodynamic changes or the presence of other lesions. Because the angiocardiogram provides a direct demonstration of the underlying anatomic abnormalities, it is the most sensitive diagnostic method for the recognition of an endocardial cushion defect.