This study was performed to compare the effect of premedicant with triflupromazine, one of the phenothizine derivatives, and more common drugs such as morphine, hydroxyzine or atropine on flow rate and mean arterial pressure. A total of 54 cases who had open heart surgery for acquired or congenital heart diseases were divided into 3 groups depending on the main premedicants. Group l : 22 cases had triflupromazine, pethidine, hydroxyzine and atropine in divided doses. These cases were induced with a small amount of thiopental, morphine and succinylcholine and maintained with either nitrous oxide(50%), oxygen, gallamine and methoxyflurane in analgesic concentrations or with morphine fractionation. Group ll: 26 cases were given morphine, hydroxyzine and atropine as premedicants. Anesthesia was induced with thiopental, morphine and diazepam and maintained with morphine, nitrous oxide and oxygen. Group lll : 6 cases were premedicated with hydroxyzine and atropine only and maintained with halothane. After induction, surface cooling was begun using a blanket, combined with internal cooling during bypass. In group l and lll rectal temperature was maintained between 28 and 32 ℃. in group ll, however, temperature was lower than other groups. After the main intracardiac procedures, rewarming was performed with combined surface and internal techniques. In most case a bypass time of longer than 1 hour was required with the longest times in group lll, 129.80±21.49 min. in duration. The longest anesthetic time was in the child group of group lll, 430±45.82min. in duration. Urine output during bypass in subgroup of methoxyflurane and morphine of group l was 8.95±0.33 and 12.15±0.36cc/kg/hr. In group ll the subgroup maintained with morphine in the adult and child and halothane, outputs were 11.63±0.14, 19.79±0.26 and 8.43±0.33 cc/kg/hr. respectively. In group lll maintained with halothane, output was 8.64±0.22mg/kg/hr. Mean arterial pressure(MAP) during bypass in most cases was maintained between 50 to 100 torr. In group l, the methoxyflurane subgroup, pressures were lower than in any other group, and higher flow rate was required than in any other group. Average MAP during cross clamp on the aorta of group l-methoxyflurane, group ll-morphine adult, group lll were 56.61±12.47, 78.79±17.33, and 74.06±19.09 mmHg respectively. MAP below 50 torr immediately after beginning bypass was more frequent in group ll(94.8%) than in other groups, and MAP above 100 torr after aorta clamping was observed more in group ll(65.2%) and in group lll(50%) than in group l(10.05%). Time to extubation was longer in group ll, the morphine subgroup, than in other groups 19.02±1.26 hours in the adult group and 20.05±2.69 hours in the child group. Post-op recovery in ICU averaged 4.17±0.65 days being longer in group l, the morphine subgroup, than in other groups. With this experience, we may conclude that group l with triflupromazine premedicants, as compared with the other groups, showed less esophageal and rectal temperature gradients during cooling and rewarming states, less acid base imbalance, better urine output, lower requirement of vasopressors or dilators to keep MAP with more flow rate in reasonable range during bypass and shorter time to extubation after surgery.