A number of groups have directed clinical and laboratory research efforts to define and delineate the limits of hypothermic circulatory arrest. The deleterious effects of cardiopulmonary bypass in small children are reviewed to place into historical perspective the impetus behind the development of hypothermic circulatory arrest. Among the advantages of deep hypothermic circulatory arrest are decreased exposure to cardiopulmonary bypass with its sequelae, improved operative field exposure, avoidance of multiple cannulas, and reduced postoperative edema. Because of concern regarding the effectiveness of the neurologic protection afforded by deep hypothermic circulatory arrest, a body of literature has developed that includes both clinical (eg, the Boston Circulatory Arrest Study) and laboratory investigations of the influence of pH strategy, hematocrit level, oxygen strategy, intermittent reperfusion, and their interaction on outcome measures. Concomitantly, changes in both cardiopulmonary bypass and circulatory arrest techniques have led surgeons to reconsider the indications for deep hypothermic circulatory arrest use in children. In the future it will be important to focus an equal degree of attention to refine methods of continuous cardiopulmonary bypass including innovative methods that allow avoidance of circulatory arrest. No clear guidelines are presently available for the congenital surgeon regarding how low flow can be reduced, at what temperature repair should be undertaken, and what duration of low flow can be used for particular circumstances of pH, hematocrit, and collateral return. Until this information is collected, the comprehensive information regarding circulatory arrest that has already been gathered allows this technique to be used more safely than innovative but unproven methods of continuous cardiopulmonary bypass.