During off-pump coronary artery bypass grafting, hypothermia increases vasoconstriction, myocardial afterload, coagulopathy and postoperative bleeding. Traditional thermoregulatory techniques do not maintain core body temperature intraoperatively. The efficacy of a commercially available, computer-controlled, water-circulating, dorsal surface, active warming system for thermoregulatory control was evaluated. All patients who underwent non-emergency off-pump coronary bypass grafting by a single surgeon in a 1-year period were studied: the thermoregulation device was used in 50 cases and unavailable for use in 19. The patients who underwent active thermoregulation demonstrated significantly improved core body temperatures compared to the controls: lowest intraoperative, 35.8 degrees C +/- 0.1 degrees C vs. 35.0 degrees C +/- 0.2 degrees C; immediately postoperative, 36.5 degrees C +/- 0.1 degrees C vs. 35.6 degrees C +/- 0.2 degrees C; and 1-hour postoperative, 36.6 degrees C +/- 0.1 degrees C vs. 35.9 degrees C +/- 0.2 degrees C. Thermoregulated patients had significantly reduced 24-hour chest tube drainage (764 +/- 38 vs. 1227 +/- 183 mL), packed red blood cell transfusions (1.4 +/- 0.2 vs. 3.3 +/- 0.7 units), time to extubation (6.8 +/- 0.5 vs. 11.4 +/- 2.3 hours), intensive care unit stay (1.3 +/- 0.1 vs. 2.0 +/- 0.3 days), and hospital stay (4.3 +/- 0.1 vs. 5.1 +/- 0.3 days).