Hypothermia : Hypothermia reduces the metabolic requirements of the body thereby reducing oxygen consumption. It also preserves high-energy phosphate stores of the body. At normal temperature, if there is circulatory arrest for three minutes, brain suffers hypoxic damage. At 30°C, this period extends up to 10 minutes. If the temperature is brought down to l8°C, this period extends up to 45 minutes. .In 1953, John Lewis used surface hypothermia up to 280C and by inflow occlusion method closed atrial septa1 defect while the heart was arrested for 5.5 minutes. Japanese surgeons started surface cooling followed by short period of core cooling to achieve deep hypothermia (l8°C) to have circulatory arrest to correct complicated intra cardiac lesions in babies. Surface cooling being a cumbersome procedure, these days both cooling and re warming are done on tile pump. In this technique of deep hypothermia and circulatory arrest (DHCA), it is safe if the period of arrest is 30 minutes or less. Between 30 minutes and 45 minutes, it is relatively safe. Above one hour, brain damage is likely to occur. In adults, the same technique is used for aortic arch aneurysms and pulmonary thrombo-endarterectomy. At the time of circulatory arrest, retrograde cerebral perfusion with cold perfusate through superior vena cava (cerebroplegia) is practised.