The primary objective of the proposed investigation is the development of an effective, safe, and clinically applicable method for the assessment of regional myocardial nutrient flood flow and for the localization and sizing of myocardial infarcts. The approach to be employed utilizes positron-emitting monovalent cations which act as K ions analogs and are actively transported into myocardial cells from the coronary circulation with high efficiency. Imaging will be accomplished by a high resolution multicrystal positron camera using multiple coincidence detection of positron annihilation radiation for collimation. A data rate capacity of 5 x 10 to the 4th power coincident events per second allows sequestional images of fractional second duration to be obtained, with spatial resolution less than 1 cm. Tracers to be studied include NH 13, plus a short half-lived tracer (T 1/2 equals 10 min) produced in the Massachusetts General Hospital cyclotron by deuteron bombardment of methane. Initial experiments in dogs show 90 percent uptake of 13NH4 plus Mn a single pass through the coronary circulation, with a half-time for biological clearance of 72 min. Scintigraphic images obtained with the positron camera show homogeneous uptake in the normally perfused ventricle following intravenous of intracoronary infusion of 13NH4 ion, and well delineated areas of decreased uptake after ligation of distal branches of the left coronary system. Systematic studies are proposed to allow: 1) radiopharmaceutical development; 2) determination of in vivo kinetics and organ distribution of NH4, K, and Rb in the dog; 3) development of optimum techniques for in vivo myocardial scanning using the positron camera (canine experimental model); and 4) determination of the feasibility and role of myocardial scanning in patients, particularly those with ischemic heart disease. Additional studies are proposed to develop improved methods of cardiac evaluation using CO labelled with C11 or O15 as a positron-emitting tracer for imaging of the intravascular compartment.