We describe a 39-year-old woman who was diagnosed as having an unusual atrioventricular septal defect with a communication from left atrium to right ventricle. A common atrioventricular junction, with partially separated right and left atrioventricular orifices, was found at transoesophageal ultrasonic examination. Both bridging leaflets were attached to the underside of the atrial septum, which was grossly malaligned relative to the ventricular septum. The shunt was exclusively from left atrium to right ventricle because of the overriding of the left atrioventricular valve, with the left component of the inferior bridging leaflet firmly fused to the ventricular septal crest.
