This program of research is directed toward the detection and the evaluation of the extent and significance (in terms of myocardial blood flow and cardiac function) of coronary atherosclerosis in patients with ischemic heart disease. It is proposed to continue to develop and improve a method to estimate quantitatively regional myocardial perfusion in patients with coronary disease using 133 xenon and a multiple-crystal scintillation camera and to validate it in experimental animals with radioactive microspheres. Measurements of regional myocardial blood flow will be made in groups of patients with different degrees of coronary atherosclerosis apparent on the angiograms to obtain information in man concerning the effects of coronary obstructions upon regional and total myocardial blood flow and blood flow reserve. The measurements will be correlated with measurements of total and segmental ventricular performance and with findings at coronary by-pass surgery and outcome. Additional protocols using the same techniques will address problems such as the pathogenesis of angina pectoris, the role of coagulation in ischemic heart disease and criteria for the selection of patients for by-pass surgery.