Cross-clamping of the descending thoracic aorta results in proximal hypertension,increase in left ventricular afterload,and impairment of distal organ perfusion. Bypass of the descending thoracic aorta is frequently advocated as an adjunct for repair of traumatic tears and degenerative aneurysms. Many methods of bypass have been proposed to provide distal perfusion and reduce left ventricular afterload during cross-clamping of the thoracic aorta. At Seoul National University Hospital, 7 patients were treated for the thoracic or thoracoabdominal aortic aneurysm using left atrium-femoral artery bypass with Bio-medicus centrifugal pump between October,1989, and January,1993. There were atherosclerotic thoracic aneurysm in 3 cases, thoracoabdominal aortic aneurysm due to chronic aortic dissection in 3 cases,aortic rupture due to trauma in 1 case. Total of 7 patients were operated by graft replacement with reimplantation of important branches. None of these cases developed severe complications and hospital death. We believe that the Bio-Medicus centrifugal pump is a simple and safe means of perfusing the lower body, kidneys, and spinal cord without necessitating heparinization.