This study sought to investigate the effects of cr and pH stat regimens on cardiac outcome during moderate hypothermic cardiopulmonary bypass. 100 patients undergoing elective coronary artery bypass grafting (CABG) were randomly assigned with respect to the target value for PaCO 2 during cardiopulmonary bypass (CPB) into 2 groups. In 50 patients the target PaCO 2 was 40 mmHg, measured at a standard electrode temperature of 37 o C while in the other 50 patients the target PaCO= was 40 mmHg, corrected to the patients nasopharyngeal temperature (lowest value reached: 32 + 0.5~163 There were no significant differences between groups with regards to cardiac outcome such as appearance of new 'Q' waves on the electrocardiogram, postoperative creatinine kinase-MB fraction, systemic vascular resistance (SVR), cardiac index (CI), need for inotropic or intra-aortic balloon pump support and the length of postoperative ventilation or intensive care unit stay. These findings support the hypothesis that CO 2 management during CPB at moderate hypothermia has no clinically significant effect on cardiac outcome.