The effects of chronic exercise and stress on the myocardium and its nutrient vessels are poorly understood. Recently our laboratory has published several studies on mechanical and biochemical adaptations in hearts of physically trained animals. The role of the coronary vasculature and coronary collaterals in these mechanical adaptations have not been elucidated. We propose to intensively study the effects of exercise on both the anatomy as well as functional capacity of myocardial vessels in the dog. We propose to study whether exercise induces development of coronary collaterals and whether these collateral channels will then have the capacity to protect the myocardium when the main coronary vessel is occluded. Aortic and coronary flow probes and arterial and left atrial catheters will be implanted in beagles which will subsequently be trained to run on a treadmill. Myocardial flow distribution in animals with both compromised and occluded coronary arteries will be determined at rest and during exertion by the radioactive microsphere technique. The effect of an exercise training program on this distribution will also be studied. Flow to visceral organs as well as skeletal muscle during exercise and the extent of adaptive changes after a training period will be evaluated. Additionally the potential benefits of a training period will be tested by studying hemodynamics and myocardial flow distribution in open-chest dogs during isoproterenol infusion and inhalation of 10 percent O2/90 percent N2 mixtures, stresses inducing peripheral vascular alterations which simulate the exercise state. Before exercise programs can be intelligently advocated for either rehabilitation or prophylaxis in coronary artery disease, these results in experimental animals should be known.