The tracer I-123-BMIPP was examined for its ability to reflect myocardial lipid metabolism. Studies in mice indicate that myocardial BMIPP uptake correlates with ATP content. Details, however, of myocardial accumulation in the ischemic period with either infarct or ischemia are not well documented. Methods: Sixteen adult mongrel dogs were investigated. The occluded left anterior descending artery (LAD) alone was reperfused to make the ischemic area, and the first diagonal branch of the LAD was kept occluded to make the infarct area. Regional wall motion was evaluated by echocardiography in the short-axial view from the epicardium. Tissue blood flow was calculated using nonradioactive colored microspheres, Changes in blood glucose levels, lipid levels and lactate extraction were examined in blood collected from the aorta and great cardiac vein (GCV). The ATP concentration and BMIPP count were determined by high-performance liquid chromatography and gamma-counter, respectively. Results: Two hours after reperfusion, blood flow decreased to 20%+/-5% in the infarct area and 64%+/-91% in the ischemic area (p <0.05), despite comparable wall-motion reduction (32%+/-5% and 42%+/-12% in the infarct and ischemic areas, respectively). BMIPP content and ATP concentration showed parallel reduction: 40%+/-7% and 75%+/-4% (p <0.05) of BMIPP and 32%+/-9% and 69%+/-7% (p <0.05) of ATP in the infarct and ischemic areas, respectively. The nonesterified fatty acid extraction, defined as {flow x ([artery]-[GCVD])}, decreased to 87%+/-5.6% during occlusion and 75%+/-20.1% 2 hr after reperfusion, as compared with the control value. Conclusion: BMIPP uptake correlated well with lipid metabolism and tissue ATP levels and may prove useful in differentiating myocardial infarction from ischemia in the acute phase of ischemic episodes.