We experienced 4 cases of open heart surgeries under preoperative diagnosis of heparin-induced thrombocytopenia(HIT). We performed operation with argatroban instead of heparin. The argatroban was administered intravenously with a bolus of 100 μg/kg. After activated clotting time(ACT)reached over 200 seconds, continuous infusion of argatroban was started, 1~2 μg/kg/min until the level of ACT over 250 in the case of off-pump coronary artery bypass grafting(OPCAB), with 6~10 μg/kg/min, or the level of ACT over 400 with the use of cardiopulmonary bypass (CPB). All cases required more than 60 minutes to achieve the target ACT level after starting the argatroban. In 1 case it was impossible to achieve target level of ACT by argatroban alone, and heparin was used concomitantly. In 1 case there was a complication of membrane occlusion of CPB. Open cardiac surgery with the use of argatroban required specific care for coagulation to complete operation.