The feasibility of double-labeling of acute myocardial infarcts with 113mIn-EDTMP [ethylenediaminetetra(methylene phosphonic acid)] and 99mTc-EDTMP was evaluated. The in vitro distributions of these tracers in acute myocardial infarcts in dogs and their selectivities for infarcted versus noninfarcted myocardium were compared. Both tracers concentrated in acutely infarcted myocardium, and there was excellent correlation between their uptakes (r = 0.88). They also provided complete separation between infarcted and uninfarcted tissue, as checked by histology. Accordingly, these agents show promise for the multiple-labeling of acute myocardial infarcts in experiments to determine the natural course of myocardial infarction and the efficacy of therapy aimed at limiting infarct size. In addition, 113mIn-EDTMP may be useful for serial scintigraphy during the early phase of acute myocardial infarction when the damage may be, at least to some extent, reversible.