The intermediate type of common atrioventricular (AV) orifice is represented by a spectrum of anomalies lying between persistent ostium primum with cleft aortic leaflet of the mitral valve and the complete form of common AV orifice. This is a study of 81 such hearts. These hearts do not have a distinct cleft in the aortic leaflet of the mitral valve, nor do they have a common valve, as seen in the complete form of common AV orifice. They may or may not have a ventricular septal defect. The surgical importance of the intermediate forms lies in the lack of sufficient valvular tissue on the left side to propertly fashion a mitral valve in many cases (41%).