A study is in progress for the purpose of examining the effects of reduced blood and oxygen supply on the function and metabolism of the mammalian heart. Investigations make use of diving seals. Recent studies in this and other laboratories have shown that the adaptations of seals and other marine mammals to diving asphyxia are specific and highly developed examples of general vertebrate adaptations to asphyxia. Specific research projects are: studies of adaptations of seal heart to asphyxial hypoxia of diving, including: myocardial metabolism, determinants of oxygen consumption, coronary blood flow and mitochondrial function in hypoxic and ischemic myocardium. Special attention is directed to the intense coronary vasoconstriction which has been found to occur during diving. This reaction takes place repeatedly for periods of 15 to 45 seconds interrupted by brief restorations of flow. This condition appears to resemble coronary vasospasm which occurs in some clinical manifestations of coronary artery disease. The seal may provide a natural model for its study. Recent results indicate that cardiac work and oxygen consumption are much reduced during diving and a significant portion of the seal's myocardial energy is derived from anaerobic metabolism.