The cardiovascular responses of aortic cross-clamping and declamping with normal and high ventricular filling pressures were compared during epidural and nitrous oxide-morphine anesthesia in 32 male patients undergoing reconstructive aortic surgery. The patients were divided into four groups. Groups I and II had lumbar epidural blocks with bupivacaine and received nitrous oxide in oxygen to breathe; groups III and IV were anesthetized with morphine (2 mg/kg) and nitrous oxide. During aortic occlusion groups I and III received Ringer's lactate at a rate which maintained mean pulmonary capillary wedge pressure (PCWP) 3 to 4 torr above pre-anesthetic values whereas groups II and IV were given Ringer's lactate rates which kept PCWP similar to pre-anesthetic values. Prior to cross-clamping mean arterial blood pressure and systemic vascular resistance were lower in groups I and II than in groups III and IV but cardiac output, PCWP, and pulmonary vascular resistance were similar in the four gropus. Cross-clamping of the aorta produced no significant change in any cardiovascular variable measured in any group. Declamping did not significantly alter any variable in groups I and III but produced moderate hypotension in group IV and severe hypotension in group II as well as significant decreases in PCWP in both groups. Our data demonstrate that aortic cross-clamping and release result in little change in cardiovascular dynamics in patients anesthetized with epidural or morphine-nitrous oxide and given balanced salt solutions intravenously in amounts adequate to increase left ventricular filling pressures prior to release of the aortic cross-clamp. Our findings also indicate that hypotension can occur in patients in whom left ventricular filling pressures are maintained at normal levels prior to cross-clamp release, especially in patients given epidural anesthesia.