Advances in cardiopulmonary bypass and cardiac surgical techniques have tremendously improved the outlook for children born with congenital heart defects. However, cardiopulmonary bypass, hypothermia, and circulatory arrest are all unphysiologic states and are associated with some morbidity, and the most significant are neurologic sequelae, which can be subtle or devastating. Circulatory arrest, often used as an adjunct to deep hypothermia, is a major contributing factor to the neurologic complications after cardiopulmonary bypass. In the last decade, techniques to avoid circulatory arrest have been introduced with a substantial decrease in neurologic sequelae.