A 45 year old man was admitted for aggravated dyspnea, abdominal distension and poor oral intake. On Echocardiogram, mitral stenosis(severe), tricuspid regurgitaion(IV), and LA thrombus were diagnosed. We used heparin with continuous infusion for prevention of systemic thrombo embolism. On the 11th day of admission, the patient showed thrombocytopenia and we suspected Heparin-induced thrombocytopenia. Hirudin was used in this case as alternative anticoagulant during cardiopulmonary bypass to prevent serious complication of heparin. The patient was recovered without any complication as postoperative bleeding or systemic thromboembolism.