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The external imaging patterns and the kinetics of infiltration of indium-111 labeled polymorphonuclear leukocytes (PMNs) occurring in the course of the inflammatory response associated with myocardial infarction were studied in dogs subjected to closed-chest anterior wall infarction. The effects of infarct age and regional residual myocardial blood flow upon PMN infiltration were investigated and quantified, and the capacity of indium-111 PMNs to image the experimental infarction was evaluated qualitatively. The epicardial accumulation of indium-111 PMNs occurred primarily in infarct zones with residual blood flow of 0.6 times normal and was maximal (14.8 ± 3.8 times normal) in the lowest blood flow zone (≤ 0.1 times normal). PMN accumulation in the endocardial infarct zones occurred in the regions with blood flow < 0.6 times normal and was maximal (26.8 ± 4.9 times normal) in the lowest blood flow zone. However, contrary to the maximal epicardial infiltration period, which occurred within the first 24 hours after infarction, the maximal endocardial infiltration occurred at 72 hours after infarction. In both endocardium and epicardium, PMN uptake was minimal at 120 hours after infarction. In vivo cardiac images were abnormal and revealed discrete, anatomically distinct areas of increased myocardial radioactivity uptake in the anterior wall of all dogs studied within 24-96 hours after infarction. All images obtained 120 hours after infarction were negative.Thus, indium-111 PMNs provide a noninvasive means of in vivo imaging of the inflammatory response to myocardial infarction and allow quantification of this response at a tissue level.