BACKGROUND & AIMS Patients undergoing cardiac surgery frequently have pancreatic damage; several factors, including tissue hypoperfusion, have been implicated. The aim of this study is to better understand the effects of decreased blood supply on human pancreas. METHODS Twenty-one consecutive patients undergoing surgery for thoracic or thoracoabdominal aortic aneurysm were studied. During surgery, the descending thoracic aorta was cross-clamped for a mean of 44 minutes (range, 15-85 minutes). Effects of the resultant pancreatic ischemia were assessed by examining the patients daily for evidence of acute pancreatitis for at least 20 days after surgery and by determining serum concentrations of amylase, pancreatic isoamylase, and lipase before clamping the aorta and at varying intervals after its release (1, 2, and 6 hours during the first day and once daily for the following 6 days). RESULTS One patient died of acute necrotizing pancreatitis. None of the others had symptoms of pancreatitis postoperatively, but all showed a significant increase in serum pancreatic enzyme concentrations soon after declamping; this peaked about 24 hours later and persisted for all 7 days of the study. A significant relationship was found between the increase in pancreatic enzyme concentrations and the aortic clamping time. CONCLUSIONS Acinar cell injury is a constant, rapidly appearing consequence of severe pancreatic ischemia, even that of brief duration; acinar cell injury is usually subclinical but may also present as severe acute pancreatitis.