Between June 1973 and March 1974, 23 infants underwent corrective cardiac surgery using profound hypothermia, limited cardiopulmonary bypass, and total circulatory arrest. In eight of these infants, the blood in the heart-lung machine was buffered to create a pH of 7.6 to 7.8 at the time of circulatory arrest. This resulted in a persistent metabolic alkalosis that required reversal with dilute hydrochloric acid administered intravenously. The remaining 15 infants did not receive buffered blood and demonstrated no metabolic alteration. In comparing this group of 23 infants to 12 infants in whom standard high-flow bypass with moderate hypothermia was used, the high-flow bypass group had metabolic acidosis as compared to those corrected with profound hypothermia, even though total bypass time was similar.