Background:In some cases, permanent reduction in cerebral functioning affects a high percentage of patients undergoing cardiovascular surgery. We studied the relationship between the results of preoperative bilateral carotid artery colour Doppler sonography and regional cerebral oxygen saturation (rSO2) during coronary artery bypass graft surgery (CABG).Materials and Methods:This study was a cross-sectional analytical study conducted with 96 candidates for off-pump CABG. This study determined the percentage of the correlation of rSO2 with demographic information, diabetes, hyperlipidemia, hypertension, myocardial infraction (MI), and smoking, and also provided information on the presence and type of plaque, intima-media thickness (IMT), and percentage of stenosis of carotid artery detected through colour Doppler sonography. Data were analyzed by the t-test, the Chi-square test, and simple linear regression.Results:In this study, the mean value of rSO2 increased after intubation compared to the mean before intubation, the difference being statistically significant (P = 0.005). A comparison of the mean rSO2 of the right side of the brain and the percentage of right carotid obstruction (stenosis of less than 50% vs. stenosis with a range of 50-69%) revealed that the mean rSO2 at the time of the partial-clamp between carotid stenosis less than 50% and carotid stenosis with a range of 50-69% was statistically significant (P = 0.043).Conclusions:There is no statistically significant correlation between rSO2 and percentage of carotid artery stenosis less than 70%. It is advised that rSO2 and carotid stenosis of greater than 70% be studied in future.