An 81-year-old woman was referred to our hospital for surgical treatment for mitral valve regurgitation, tricuspid valve regurgitation and atrial fibrillatory bradycardia. The platelet count on admission was 4.9 x 10(4)/microl. and the results of other studies were compatible with idiopathic thrombocytopenic purpura. Although we performed high-dose transvenous immunoglobulin infusion (400 mg/kg/day) for 5 consecutive days, the platelet count showed no remarkable change. Because of progression of heart failure, we underwent cardiac operation under thrombocytopenic condition. Intra and post-operative platelet transfusion might contribute to postoperative course uneventful without bleeding tendency. In this case, high-dose immunoglobulin therapy was not effective. However the operative course was satisfactory with adequate surgical hemostasis and platelet transfusion.