 The study will enroll infants and children who have suffered a cardiac arrest while out of the hospital. Randomization must occur within 6 hours of return of spontaneous circulation. Participants will be randomly assigned to receive either therapeutic hypothermia or therapeutic normothermia. Participants receiving therapeutic hypothermia will have their body temperature reduced to between 32 to 34 Celsius C and will remain at this temperature for 2 days. Their body temperature will then be slowly increased to the normal temperature of 36 to 37.5 C, which will be maintained until 5 days after the cardiac arrest. Participants receiving therapeutic normothermia will have their normal temperature maintained between 36 to 37.5 C for 5 days after the cardiac arrest. Special temperature control blankets will be placed to maintain body temperature in the assigned range. After 5 days, each participants temperature will be managed by their medical care team. 