Atrioventricular septal defect with a well developed primary component of the atrial septum ("septum primum").

A heart is described with an atrioventricular septal defect in which the lower part of the atrial septum ("septum primum") was well developed and in which superior and inferior bridging leaflets were attached neither to the crest of the ventricular septum nor the inferior rim of the atrial septum. Diagnostic pre-operative angiographic and echocardiographic features and the method of surgical correction are outlined.