Twenty-three patients undergoing elective coronary artery bypass graft surgery with moderate hypothermic bypass, under opiate-benzodiazepine anaesthesia were investigated during the first 7 h following surgery. Patients with recent myocardial infarct (< 6 weeks), reduced left ventricular ejection fraction (< 40%) or requiring inotropic support were excluded. During the first 3 h after surgery, higher oxygen uptake and oxygen extraction ratio were found in shivering patients (n = 5) compared with non-shivering patients (N = 16). A significant relation was found between oxygen uptake and the oxygen extraction ratio for the pooled data (R = 0.80 and 0.87, in shivering and non-shivering patients, respectively) as well as for the individual patients. A weaker relation was observed between cardiac output and oxygen uptake. The lack of adequate circulatory compensation could be related to the myocardium, surgical trauma, cardioplegic arrest and to peripheral vasoconstriction.