The hemodynamic consequences and myocardial blood flow alterations associated with cross-clamping of the thoracic aorta were studied during pentobarbital (control), halothane (1 MAC), and isoflurane (1 MAC) anesthesia in dogs with a critical stenosis of the left circumflex coronary artery. Aortic clamping at the level of the diaphragm resulted in significant and equivalent increases in mean aortic pressure and left atrial pressure during the control clamp, halothane clamp, and isoflurane clamp periods. Likewise, aortic clamping resulted in a significant and equivalent decrease in cardiac output during control-clamp, halothane clamp, and isoflurane clamp. Myocardial contractility as assessed by dP/dt was depressed during halothane and isoflurane anesthesia when compared with control, but no further change in contractility was associated with aortic clamping. No signifcant alterations in regional or transmural myocardial bloc flow were found with halothane or isoflurane anesthesia, c with aortic clamping during halothane or isoflurane anesthesia. It is concluded that there are significant hemodynami consequences associated with aortic clamping, that neithe halothane nor isoflurane anesthesia alters these consequences when compared with pentobarbital anesthesia alone and that the deterioration in myocardial function observe during aortic clamping with halothane and isoflurane anesthesia cannot be attributed to any maldistribution of myocardh blood flow.