Background: Cardiac surgery aggravates a vital inflammatory response that endures into the postoperative period. Methods: We compared the effect of morphine and fentanyl as part of a balanced anesthetic technique on the inflammatory reaction the occurs in cardiac valve replacement surgeries after cardiopulmonary bypass (CPB). Methods: Patients are randomized to either morphine group (M) (n=15),received morphineIV(0.1mg/kg)at anesthesia induction and then(1-2mg/h) till end of surgery and arrival to the ICU or fentanyl group (F)(n=15),received fentanyl IV(5μg/kg)at anesthesia induction and then(1μg/kg/h)until end of surgery and arrival to the ICU. Serum concentrations of interleukins(IL-6 and IL-10) and expression of neutrophil surface adhesion molecules(CD11b,CD11c,andCD18)were measured immediately before the start of CPB(baseline)(T1),4 hrs post-CPB(T2),and 24 hrs after baseline measurements.Temperatures were measured on arrival to the ICU(Temp baseline),and every 2 hrs for the next 12hrs in the ICU(Temp1-Temp6).The increase in biomarkers were significantly attenuated in (M) compared to the (F) at 4hrs and 24hrs post-CPB(P<0.05). Results (Table1): The reduction in adhesion molecules expression was significantly more in the (M) than in the (F) at 4hrs and 24hrs post-CPB(P<0.05).The incidence of postoperative hyperthermia(body temperature>38.0°C)was significantly higher in (F).In (M)only one patient suffered from postoperative hyperthermia where in (F) even patients were suffered. Conclusion: We concluded that, the use of morphine when compared to fentanyl as a part of a balanced anesthetic technique in valve replacement surgery after CPB, can allow better hemodynamic stability, attenuates the release of interleukins, produce a greater reduction in adhesion molecule expression and reduce the incidence of postoperative hyperthermia without affecting the duration of tracheal intubation.