The mental strain of a cardiac surgeon may differ when he performs coronary surgery from and when he only assists in performing coronary surgery. In 50 selected cases of on-pump heart arrested coronary artery bypass grafting (CABG), an attending-consultant surgeon performed 30 procedures of CABG (Group A) and an attending-consultant surgeon supervised the remaining 20 cases of CABG performed by two resident surgeons (Group B). Intraoperative Holter electrocardiograms of the attending-consultant surgeon were recorded and analyzed for heart rate variability (HRV). In Group A, the ratio of low frequency to high frequency was at a peak in the beginning of the operation and gradually decreased toward the end of the operation. In Group B, the ratio of low frequency to high frequency was at a peak in the phase of aortic cross-clamp, coronary anastomosis, and unclamping. When an attending-consultant surgeon performed the operation himself, the most anxious part of the operation was at the beginning and thereafter the level of anxiety gradually declined. In contrast, when he assisted a resident, the highest level of anxiety was when the aortic cross-clamp was in place and out of place and during the coronary anastomosis.