Atrial septal defects (ASDs) are a common congenital abnormality, and operative repair is a routine, safe procedure. Diversion of the inferior vena cava (IVC) into the left atrium is an unusual complication following ASD closure. We report a case that illustrates the problem created by this right-to-left shunt. A middle-aged woman underwent ASD repair. She developed hypoxemia postoperatively. A transthoracic echocardiogram confirmed a right-to-left shunt, found only with agitated saline injected into the femoral vein, not into the basilic vein. Surgical reexploration revealed a residual ASD diverting IVC flow into the left atrium, which was repaired with a pericardial patch. Echocardiography with agitated saline injected from the femoral vein is an easy method to diagnose this uncommon complication.