Heparin-induced thrombocytopenia (HIT) is a life-threatening side effect of heparin therapy. We report an open heart surgery with cardiopulmonary bypass( CPB) using argatroban as an anticoagulant for a patient with HIT. A 72-year-old male with a history of percutaneous coronary intervention 5 years ago, was admitted to our hospital due to congestive heart failure and heparin 10,000 units/day was administered. At 10th hospital day, his platelet count was significantly decreased and antibodies positive for type II HIT was found, so he was diagnosed HIT. Echocardiogram and coronary angiography revealed severe functional mitral regurgitation and coronary stenosis. At 24th hospital day we performed coronary artery bypass grafting( CABG) and mitral valve replacement (MVR) with CPB using argatroban as an anticoagulant. During CPB, we monitored the activated clotting time (ACT) to adjust the dose of argatroban. Though the surgical procedure itself was uneventful. We required about 4 hours to achieve adequate hemostasis after CPB. Postoperative course was uneventful.