The use of deep hypothermic cardiopulmonary bypass (DHCPB) with or without deep hypothermic circulatory arrest (DHCA) has substantially improved operating conditions for children undergoing congenital heart surgery, resulting in improved survival and reduced cardiac morbidity. As overall surgical outcome has improved, neuropsychiatric dysfunction has become a more prominent and visible complication of the congenital heart patient. Recent reports suggest that transient and permanent neuropsychiatric injuries occur in as many as 25% of all infants undergoing hypothermic cardiopulmonary bypass with or without circulatory arrest. 1 , 2 This uncomfortably high incidence of neuropsychiatric impairment is becoming a major focal point for current research into the mechanism of cerebral injury during CPB. Currently the most effective means of protecting the brain from CPB-or DHCA-induced injury is hypothermia. 3-6 Hypothermia reduces cerebral blood flow and metabolism and preserves cellular stores of high-energy phosphates. The hypothermic methods that can be employed—either moderate hypothermia, deep hypothermia, or deep hypothermia with circulatory arrest—have differing effects on cerebral physiology and should be considered separately.