A 62-year-old woman who underwent an aortic valve replacement for severe aortic valve stenosis developed postoperative thrombocytopenia and adult respiratory distress syndrome, simultaneously. Both complications resolved promptly after discontinuing heparin therapy. The presence of a heparin-related antiplatelet antibody was detected by in vitro testing. The time course of clinical events suggests the possibility of a heparin-induced, immune-mediated injury to both the pulmonary vascular endothelium and the platelet membrane as an underlying pathophysiologic mechanism.