Background: A debate has appeared in the recent literature about the optimum rewarming strategy (slow vs. rapid) for the best brain function. This study was designed to compare the effect of slow versus rapid rewarming on jugular bulb oxygen saturation (SjO2) in adult patients undergoing open heart surgery. Materials and Methods: A total of 80 patients undergoing valve and adult congenital heart surgery were randomly allocated equally to rapid rewarming group 0.5 (0.136)°C/min and slow rewarming group 0.219 (0.055)°C/min in jugular bulb sampling was taken before, during and after surgery. Surgery was done at cardiopulmonary bypass (CPB) temperature of 28-30°C and rewarming was performed at the end of the surgical procedure. Results: CPB time, rewarming period were signifi cantly longer in the slow rewarming group. Signifi cant difference was observed in the number of the desaturated patients (SjO2 ≤ 50%) between the two groups; 14 (35%) in rapid rewarming versus 6 (15%) in the slow rewarming group; P = 0.035 by Fisher’s exact test. Conclusions: Slow rewarming could reduce the incidence of SjO2 desaturation during rewarming in adult patients undergoing open heart surgery.