The CAVC defect results from complete failure of fusion between the superior and inferior endocardial cushions during early embryogenesis. CAVC is characterized by a primum ASD that is contiguous with a posterior (or inlet) VSD and a single common AV valve. The single AV valve is often associated with regurgitation. CAVC defects are classified according to relative ventricular size. In balanced CAVC (shown here), the ventricles are relatively equal in size and are amenable to biventricular repair. In unbalanced (not shown), there is hypoplasia of either the right or left ventricle, most commonly the left.
