This chapter describes the incidence, mechanisms and possible consequences of hypothermia during cardiac surgery, including protection against ischaemia, alteration of the coagulation cascade and the inflammatory response. Various temperature-specific topics related to cardiac surgery are discussed, including the use of hypothermia or normothermia during cardiopulmonary bypass, and the temperature reached during rewarming at the end of cardiopulmonary bypass and its deleterious consequences for the brain (postoperative neurocognitive dysfunction). Various locations for monitoring body temperature and their correlation with the central core temperature are evaluated, as is the correlation between oxygenation of the brain and oxygen extraction monitored at the jugular bulb. Modern cardiac techniques, such as off-pump surgery and minimal extracorporeal circulation, and their implications for temperature preservation are discussed. Finally, a protocol is proposed that combines mild intra-operative hypothermia with peripheral active warming in order to avoid the need for fast, intense rewarming, thus avoiding the potential incidence of brain damage.