We reported a case of aortic valve replacement in a patient with chronic idiopathic thrombocytopenic purpura (ITP). We used high-dose intravenous gammaglobulin therapy (400 mg/kg/day) for five days to increase the platelet prior to the operation. The number of platelet was 8-10 x 10(4)/microliters at admission and it was increased to 23 x 10(4)/microliters before surgery. Aortic valve was replaced to SJM#21A prosthesis using cardiopulmonary bypass. The platelet was transfused after the bypass. Perioperative hemorrhage was moderate and postoperative course was uneventful. We believe that high-dose intravenous gammaglobulin therapy for ITP is effective to minimize perioperative hemorrhage for open heart surgery.