Moderate hypothermia of 30 C in dogs has been shown to diminish oxygen consumption by approximately 50%.1 In addition, we have demonstrated that after division of the circumflex coronary artery in normothermic dogs, perfusion of the distal vessel with only 10 ml. per minute of oxygenated blood will maintain the heart in a normal sinus rhythm.3 Thus, one might expect that after ligation of this artery moderate hypothermia would increase the survival rate of these animals. Haeger5 in 1959 ligated an unspecified coronary artery in 3 groups of dogs. In the first group, the artery was ligated in normothermic animals with a resultant 94% survival rate. The second group of dogs were made hypothermic. Ligation of the artery in these animals was followed by a 65% survival. The third group consisted of hypothermic dogs whose hearts were arrested with acetylcholine. Ninty-six per cent of these survived ligation