Objective The present study was designed to attempt a continuous assessment of cerebral autoregulation by continuously monitoring jugular venous bulb oxygen saturation (SjO 2) in patient undergoing cardiac operation. Methods Twenty-four patients undergoing cardiac surgery under cardiopulmonary bypass (CPB) were included. Among them 16 were male, 8 female. No neuropsychological deficit was found in any of them before or after operation. Patients had neither diabetes mellitus nor immunological diseases. Normocapnia was maintained during operation. SjO 2 and other routine parameters, such as blood pressure, temperature, heart rate, pulmonary atery pressure and cardiac output etc were monitored and recorded continuously via a computerized anesthetic recording system. The numerical data of SjO 2 and mean arterial pressure (MAP) were sampled every 30s. Correlation between SjO 2 and MAP was evaluated before, during and after CPB. According to the slope "a" of the regression line "SjO 2= b + a MAP", cerebral autoregulation was estimated. The cerebral autoregulation was taken as deteriorated if the two parameters were highly correlated with a ≥0.4, showed as dysautoregulation (+). Those with a