We report an unusual thromboembolic event occurring during severe heparin-induced thrombocytopenia. A left intraventricular thrombus was diagnosed as the source of multiple arterial emboli, resulting in an initial cerebrovascular event and subsequent bilateral acute lower extremity ischemia requiring emergency surgery. No underlying heart disease was detected. Pathologic examination of the embolectomy specimen revealed fibrin platelet aggregates with rare white and red blood cells, consistent with a "white thrombus." We conclude that routine monitoring of platelet count should be performed in all patients receiving heparin to identify promptly individuals who have heparin-induced thrombocytopenia, and when thromboembolic complications occur in this setting, echocardiography is indicated to identify possible intracardiac sources for emboli, even in patients with previously known structurally intact hearts.