BACKGROUND The coexistence of abnormalities in both atrioventricular and ventriculoarterial junctions occasionally represents a formidable challenge to the surgeon. The association of common arterial trunk with atrioventricular septal defect is such an example. To date, only two reports have described successful operative outcome. This paucity of success might reflect the anatomical complexity that could prevent favorable results. METHODS We reviewed six specimens with common arterial trunk and atrioventricular septal defect, focusing on how to establish a nonobstructed connection between the left ventricle and the truncal valve. RESULTS In all cases, the common trunk arose exclusively from the right ventricle, and the only exit from the left ventricle was the ventricular component of the septal deficiency. In particular, the preferential route was limited to a space below the superior bridging leaflet that did not have any tendinous cords inserting onto the ventricular crest, in contrast to the inferior bridging leaflets that were always tethered to the crest with many short cords. Accordingly, the size of potential left ventricular outflow depended on the shape of the anterosuperior margin of the ventricular crest below the superior bridging leaflet. The potential outflow was narrower than the truncal valvar area in all hearts but one having extensive anterosuperior excavation of the ventricular crest, suggesting the necessity of septal enlargement had anatomical repair been attempted during life. CONCLUSIONS Owing to the unique ventriculoarterial connection, the surgeon, considering anatomical repair, needs to pay attention to the anterosuperior margin of the ventricular scoop, which determines the adequacy of left ventricular outflow size.