 The overall postoperative mortality rate for cardiovascular surgery is 2.2, but is much higher for thoracic aortic aneurysm surgery 8-10 for elective repair, 25-50 for ruptured thoracic aorta aneurysm repair. The major risk factor for thoracic aortic aneurysm surgery related mortality is post-operative ARF requiring dialysis. When thoracic aortic aneurysm surgery is complicated by acute renal failure, the mortality rate worsens to 50. Thus, identifying ways to prevent acute renal failure may have a major impact on the outcome of cardiovascular surgery. A retrospective study of the use of nesiritide in cardiovascular surgery patients by our group has demonstrated a tendency towards a decreased incidence of renal failure and mortality, when the medication is used prophylactically. 