The authors describe the case of a man with ischaemic heart disease after revascularization of the myocardium by an aortocoronary bypass using extracorporeal circulation. The early postoperative course was complicated by perforation of a gastric ulcer. The condition was successfully resolved by an urgent operation, suture of the perforated stomach with toilet of the abdominal cavity. In the discussion the authors analyze the causes of the possible development of gastrointestinal complications after cardiac surgery, in particular the influence of extracorporeal circulation and other specific effects during cardiac surgery and during the immediate postoperative period.