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Summary: In a porcine model of brief ischemia leading to reversible stunning in the absence of tissue necrosis, we demonstrated delayed release of cardiac troponin I (cTnI) that exceeded the 99th percentile for normal animals 60 min after reperfusion and rose to readily detectable levels 24 h later. Although tissue analysis at 60 min showed no evidence of infarction, TUNEL staining demonstrated isolated myocytes undergoing apoptosis, which was absent after 24 h. These results demonstrate that cTnI elevations occur after ischemia of a duration that is insufficient to produce myocyte necrosis and reflect myocyte injury associated with apoptosis in the absence of pathological evidence of infarction. Key Words: cardiac troponin I, cardiomyocyte apoptosis, myocardial ischemia, myocardial stunning