FIGURE 6. (A) On right, TTC-stained 0.5-cm section of myocardium 24 h after occlusion shows significant necrosis. On left, electronic autoradiography shows absence of ⁶⁴Cu-ATSM retention in this region 24 h after occlusion, consistent with necrosis. Autoradiograph also shows area of increased ⁶⁴Cu-ATSM accumulation bordering necrotic regions, indicating hypoxic zone surrounding necrotic zone. (B–D) Graphs show MBF (B), 1/k_mono retention (C), and 1/k₄ retention (D) as ratios of LADR to NLR at 3 and 24 h. (C and D) *Cu-ATSM myocardial retention patterns reveal that tracer retention did not increase 3 h after LAD occlusion in dogs with small infarcts but increased significantly in dogs with decreased MBF in LADRs. At 24 h, MBF in LADRs was severely reduced in 3 of 4 animals (B). Retention values obtained from kinetic modeling (D) show that, in animals with severely reduced MBF at 24 h, retention in LADR decreased. Conversely, retention increased in the only animal (dog 11) in which MBF remained within 80% of normal. This pattern is consistent with necrotic tissue and with infarct size observed through postmortem staining. These data also demonstrate that retention and clearance of *Cu-ATSM are not related to perfusion.