The aim of the study was to identify causes for perioperative stroke in cardiac surgery in order to reduce its occurrence. From 1989 to 1994, 3593 open heart operations were performed in adult patients. In 59 patients carotid endarterectomy for high grade stenosis was combined with the cardiac operation. There were a total of 68 (2%) focal strokes, 41 of which were considered minor and 14 major; 13 were lethal. The etiology of the 27 major and lethal events was most probably an embolus from the ascending aorta (6), from the ascending aorta or a cardiac valve (5), a thrombus in the left heart (6), air (1), cardiac arrest and resuscitation (4), cerebral hemorrhage (1), preoperatively unknown but high grade internal carotid stenosis (3), and a 50% stenosis of both internal carotid arteries preoperatively known but not operated on (1). There were 2 minor but no major neurologic complications in patients undergoing a combined carotid and cardiac procedure. A wide indication for preoperative neuroangiologic examination, echocardiography and careful intraoperative management may help to identify sources of possible emboli. Endarterectomy of high grade carotid stenosis is recommended simultaneously with the cardiac procedure.