Although large doses (0.5–3.0 mg/kg, iv) of morphine plus oxygen have little effect on cardiovascular dynamics in critically ill patients undergoing open-heart or other major operative procedures, incomplete amnesia and awareness are not infrequent complications of this technique.1Use of nitrous oxide as a supplement during morphine anesthesia prevents awareness but results in significant cardiovascular depression.2,3Diazepam and droperidol have also been employed as supplements during morphine anesthesia to prevent awareness! However, the cardiovascular effects of these drugs after large doses of morphine have not been investigated. This study was undertaken to determine the hemodynamic effects of two 5-mg doses of diazepam or two 2.5-mg doses of droperidol in receiving 1.5–2.3 mg/kg morphine for open heart or major vascular operations.