Trained dogs with chronically implanted catheters and left ventricular (LV) pressure transducers were anesthetized with 2.3 per cent (1 + MAC) and 3.6 per cent enflurane. Left ventricular function and metabolism were studied while the dogs were awake and during exposure to the two anesthetic concentrations. Enflurane depressed LV function in a dose-dependent fashion. Myoeardial blood flow and oxygenation mirrored the functional changes. Mayocardial oxygen extraction decreased and lactate extraction incrcased during enflurane anesthesia, suggesting adequate oxygen delivery to the myocardium. Low concentrations of halothane in the same dogs on different days had similar effects. However, 2 MAC halothane resembled 1.6 MAC enflurane, suggesting that the cardiovascular dose-effect curve for enflurane is steeper than that for halothane. Both anesthetics produce dose-dependent negative inotropic effects in the intact dog, accompanied demand. Contrary to previous suggestions, enflurane appears to be at least as depressant to the dog heart as halogthane.