Objective: Systemic embolism is a serious complication after classical orthotopic transplantation, presumably originating from enlarged left atrium. We speci®cally studied this problem after classical and modi®ed bicaval transplantation. Methods: Between December 1985 and March 1999 we consecutively performed 72 classical and 106 modi®ed heart transplantation. Modi®cation included bicaval anastomosis and recipient left atrium maximal reduction. Mean age was 47 years. All the patients received an antiplatelet therapy and were routinely followed. When clinical signs of systemic embolism were present, a neurological evaluation and transesophageal echocardiography were done. Sixty matched patients (30 of each group) had comparative transesophageal echocardiography study, at least 6 months after transplantation. Results: Perioperative mortality was 17.4%. Mean follow-up was 6.8 2 1 /47 years. All patients were in sinus rhythm. Among 147 survivors, 11 patients who underwent classical transplantation had a systemic embolism, 1 month to 12 years after transplantation, 15.3%, (11/72). Two limb ischemia and one mesenteric ischemia (needing surgery), seven strokes (one death, two permanent neurological de®cit). There was no systemic embolism in the modi®ed technique group (P ˆ 0:013). Left atrial comparative transesophageal echocardiography study showed a larger left atrial surface in classical transplantation. 33 ^ 4 cm 2 versus 20 ^ 3 cm 2 in a modi®ed technique, P ˆ 0:01. Spontaneous echo contrast was present in 56% of classical technique group associated with atrial thrombosis in nine patients, there were no atrial thrombosis in modi®ed technique group and spontaneous echocontrast was present in 0.5% (P ˆ ,0:001). Conclusion: The occurrence of systemic embolism, left atrial spontaneous echocontrast and thrombosis when using classical technique, and the absence of these complications with the bicaval technique justi®ed the use of this method. Our experience with atrial thrombosis and spontaneous echocontrast rises the question of anticoagulation in classical transplantation. q