Atrial septal defect with right to left shunt despite normal pulmonary artery pressure.

A 74 year old woman had right to left shunting through an atrial septal defect despite normal right heart pressures. Acute volume expansion temporarily reduced the shunt. Contrast echocardiography and angiography demonstrated that this shunting occurred almost exclusively from the inferior vena cava. At surgery a redundant flap of septum secundum was found that was adjacent to the inferior vena cava orifice, intercepting its blood return like a spinnaker and shunting it into the left atrium.