Topical cardiac cooling plays an important part in maintaining myocardial hypothermia during cardiac operations under hypothermic cardioplegic arrest. We have compared two systems of topical cooling in which the cooling fluid is recirculated. In one system the cold fluid circulates through a sealed plastic cooling pad wrapped around the heart; in the other it is sprayed over the surface of the heart. In dogs undergoing 60 minutes of hypothermic cardioplegic arrest, the cooling pad was ineffective: it did not adequately cool the anterior left ventricular wall or the interventricular septum. Under the same conditions, the spray system produced myocardial temperatures 6 degrees to 12 degrees C lower than the cooling pad system. In limited clinical tests, the cooling pad was unable to sustain overall myocardial hypothermia and there was difficulty in maintaining contact between the heart and the pad during coronary operations. Since the topical spray can maintain profound global myocardial hypothermia regardless of the position of the heart, we conclude that it is superior to the cooling pad system.