Heat Exchangers :  This is an integral part of cardio pulmonary bypass and is designed to cool and warm the perfusate. non-sterile water from ice bath or warm water passed through the tubing made of stainless steel or aluminium is immersed in blood flowing in opposite directions. (Counter current heat exchange). Rapid cooling is desirable at the beginning of perfusion with the circulating water kept at 0 degree C. Rewarming has to be done -slowly to avoid damage to blood elements and to avoid bubble formation in the perfusate. The temperature gradient between water and blood should always be less than 1 O°C, while rewarming. The maximum temperature of the bath should be less than 42^OC.