The optimal degree of hemodilution during profoundly hypothermic CPB remains controversial, and widely dissimilar hemodilution studies have evolved at centers that perform infant cardiac surgery. HCT, a measurement of the volume of red blood cells, is of interest in cardiopulmonary bypass. Higher HCT levels expose individuals to the risks of microvascular occlusion (blockage in the small blood vessels), while lower HCT levels may critically limit oxygen delivery to the brain and other organs. Preliminary research suggests that higher HCT levels provide superior brain and myocardial protection, but there have not been any studies that report on outcomes after usage of higher versus lower HCT levels.