This study was performed to investigate the relation between total oxygen consumption (VO2) and the velocity of reheating in patients undergoing cardiopulmonary bypass with hypothermia. A total of 17 males undergoing this procedure were studied prospectively (mean age: 63 years, range: 52-72); during surgery they were cooled at 28 degrees C whole-body temperature. Before rewarming, patients were divided at random in two groups. Group A (n = 8) was reheated between 10 and 25 minutes, and group B (n = 9) between 26 and 50 minutes. In group A, VO2 expressed in ml.min-1 x m-2 increased from 76.6 +/- 6.99 at 28 degrees C until 100.0 +/- 6.72 at 34 degrees C; in group B increased from 68.4 +/- 4.55 until 129.1 +/- 4.73 at similar temperatures (analysis of variance: p < 0.01 at 28 degrees C). A greater VO2 in group B could indicate that slow rewarming would cause an even distribution of temperature with enough time for tissues to rid of their oxygen debt.