Fifty-eight patients studied were anesthetized with diazepam, pancuronium, and a moderate dose of fen-tanyl; 99 sets of multiple hemodynamic variables were measured after sternotomy and before cardiopulmonary bypass. The relationship between oxygen consumption (Vo2) and oxygen delivery (Do2) was studied. The critical value of D02 was identified to be 330 ml/min·M2 or 8.2 ml/min kg by an analysis of the regression lines. When Do2 was less than 330 ml/min·M2, the value of Vo2 decreased in proportion to a decrease in Do2 and Vo2 was expressed as: Vo2 = 0.36 × Do2 –11.20 (n=30, r=0.77, p < 10–6). At Do2 greater than 330 ml/min·M2, Vo2 values plateaued at 109 ± 16 (SD): n = 69; r = –0.02, p > 0.05; while mixed venous oxygen tension (PJOURNAL/ccme/04.02/00003246-198308000-00011/ENTITY_OV0456/v/2017-07-20T220504Z/r/image-pngO2) decreased in proportion to the decrease in Do2, suggesting compensatory increase of oxygen extraction. A decrease of Vo2 at Do2 less than 330 ml/min M2 suggests tissue oxygen deprivation occurred.