Background. Which blood gas strategy to use during deep hypothermic circulatory arrest has not been resolved because of conflicting data regarding the advantage of pH-stat versus α-stat. Oxygen pressure field theory suggests that hyperoxia just before deep hypothermic circulatory arrest takes advantage of increased oxygen solubility and reduced oxygen consumption to load tissues with excess oxygen. The objective of this study was to determine whether prevention of tissue hypoxia with this strategy could attenuate ischemic and reperfusion injury. Methods. Infants who had deep hypothermic circulatory arrest (n = 37) were compared retrospectively. Treatments were α-star and normoxia (group I), α-star and hyperoxia (group II), pH-stat and normoxia (group III), and pH-stat and hyperoxia (group IV). Results. Both hyperoxia groups had less acidosis after deep hypothermic circulatory arrest than normoxia groups. Group IV had less acid generation during circulatory arrest and less base excess after arrest than groups I, II, or III (p < 0.05). Group IV produced only 25% as much acid during deep hypothermic circulatory arrest as the next closest group (group II). Conclusions. Hyperoxia before deep hypothermic circulatory arrest with α-stat or pH-stat strategy demonstrated advantages over normoxia. Furthermore, pH-stat strategy using hyperoxia provided superior venous blood gas values over any of the other groups after circulatory arrest. (C) 2000 by The Society of Thoracic Surgeons.