[en] While oxidation of fatty acid declines or even ceases during ischemia, the recovery of myocardial fatty acid metabolism after transient ischemia has remained largely unexplored. Using C-11 palmitic acid as a tracer of myocardial fatty acid metabolism, we evaluated in open chest dogs the myocardial retention and subsequent tissue clearance of intracoronary injected C-11 palmitic acid at control and up to 3 hours after a 20 min occlusion of the LAD. In animals with permanent occlusion, the relative size and halftime of the early clearance curve component, representing oxidation of C-11 palmitic acid, differed markedly from control and did not change with ongoing ischemia. In animals with a 20 min coronary occlusion, the relative size of the early C-11 clearance phase was still significantly depressed at 20 and 90 min of reperfusion but had returned to control at 180 min. The tissue C-11 clearance halftimes remained significantly prolonged throughout the entire reperfusion period. Regional function in the reperfused segments monitored with ultrasonic crystals recovered only slowly and was still less than control after 3 hrs of reperfusion. These data indicate that myocardial fatty acid metabolism after transient ishemia recovers slowly. C-11 palmitic acid in conjunction with Positron-CT may thus be useful for studying regional fatty acid metabolism noninvasively following an ischemic injury and may be helpful in identifying reversible tissue injury