A 64-year-old man was presented to another hospital with bleeding from the upper jaw with a platelet count of 0.1 x 10(4)/microl one year ago, and idiopathic thrombocytopenic purpura complicated with aortic stenosis and regurgitation was diagnosed. Corticosteroid administration was initiated and the patient was admitted to our hospital for surgery two months after confirmation of symptoms associated with cerebral ischemia. Corticosteroid was administered for one year until the day of surgery, and aortic valve replacement was performed with a platelet count of 8.4 x 10(4)/microl. During surgery, bleeding tendency with decreased platelets was confirmed, which was corrected with intraoperative platelet transfusion, postoperative gamma-globulin administration, and postoperative oral corticosteroid administration. Caution must be exercised against perioperative bleeding tendency in open heart surgery, even when platelet count is maintained using small amounts of preoperative corticosteroid.