Twenty-two patients undergoing coronary artery bypass surgery underwent postoperative measurement and recording of jugular venous oxyhaemoglobin saturation (SjO2) with desaturation defined as a value of less than 50% for 5 min or longer. Fifteen of the 22 patients monitored experienced desaturations. An average of four episodes were experienced by those 15 patients (range 1-14). The mean duration of a single episode was 46 (range 5-212) min whilst mean total duration of desaturation was 175 (range 5-570) min. The mean duration of desaturation in the 15 patients, expressed as a percentage of monitored time, was 21.1% (range 0.58%-61.96%). SjO2 desaturation, possibly indicating cerebral hypoperfusion, occurs in the early post-operative period following cardiac surgery.