Real-time 800 phased-array two-dimensional sector echocardiography was used in 44 patients with atrioventricular (AV) canal defect. Anatomic details were surgically confirmed in 33. The apex view allowed visualization of atrial and ventricular portions of complete AV canal defects, with the common AV valve structures between the defects. The apex view also allowed us to differentiate divided and undivided, attached and free-floating common anterior valve leaflets to distinguish types A, B, and C complete AV canal defects. With the apex view, the ostium primum atrial septal defect and the attachment of the AV valve to the crest of the ventricular septum were observed in partial AV canal defect. Short-axis views revealed the cleft in the anterior leaflet of the mitral valve. The rapid and precise definition of anatomic details by this method has eliminated many of the difficulties in diagnosing this defect by M-mode echocardiography.