We describe a case of severe acute aortic regurgitation in a 60-year-old woman due to spontaneous avulsion of an aortic valve commissure. She presented with spontaneous bleeding and a platelet count of 4 000/microl caused by idiopathic thrombocytopenic purpura and developed acute heart failure and respiratory insufficiency. Preoperative transesophageal echocardiography was not diagnostic for the exact mechanism of aortic regurgitation. She received a 2-day course of intravenous immunoglobulin (0.5 mg/kg/d) to increase platelet count. At operation detachment (avulsion) of the commissure between the left and the right coronary cusp was evident. Aortic valve repair was performed with resuspension of the commissure. The postoperative course was uneventful. During a 24-month follow-up period, the patient has remained in NYHA class I.