Following a clinical experience of too cardiac operations in infants during deep hypothermia, as low as 15°C, the authors have designed a new bath for the procedure which incorporates several improvements over those used previously. The device described allows continuous cooling or rewarming of the patient at any stage of the operation by addition of more cold or hot water as required. It is possible to operate with the patient prone or on the side at any level of hypothermia, and while using heart lung bypass: The construction facilitates the even distribution of the circulating water, and a thermostatic control allows the temperature to be fixed at any level required