Sixty-year-old woman admitted with dyspnea and cough. Three weeks ago she underwent primary stenting for acute anterior myocardial infarction and recieved antiplatelet therapy (clopidogrel). Echocardiography and left ventriculography revealed left ventricular segmental dysfunction at anterolateral-apical region but no thrombus. On last admission, despite the clopidogrel therapy, echocardiography showed giant-partly mobil thrombus obliterated half of the left ventricle. Slow infusion of thrombolytic therapy was given and complete lysis occurred with uneventful course. Disclosure of such a rapidly evolving giant left ventricular thrombus in the clopidogrel non-responder is a rare clinical problem with potentially catastrophic consequences. Slow infusion of thrombolytic therapy may be effective and life saving.