Unusual "midseptal" sinus venosus defect.

An unusual case of an interatrial communication similar to a sinus venosus defect associated with an overriding pulmonary venous chamber is reported. There was no direct connection of the pulmonary venous system with either the superior vena cava or the low right atrium, as is usual with sinus venosus defects. This defect may represent the result of a sinus venosus defect associated with cor triatriatum.