The purpose of this study was to determine if biochemical, functional, and ultrastructural abnormalities persist in nonnecrotic postischemic myocardium salvaged by coronary reperfusion. Anesthetized dogs were subjected to 15 min of occlusion of the left anterior descending (LAD) coronary artery followed by 3 days of reperfusion. Biopsies were obtained for measurement of adenosine 5'-triphosphate (ATP) and creatine phosphate (CP) nmol/mg protein), and regional function was evaluated using sonomicrometry. Myocardial ATP concentration after 15 min of occlusion was 37 +/- 1 nmol/mg cardiac protein in nonischemic subendocardium and 19 +/- 2 nmol/mg in ischemic subendocardium. After the hearts underwent 90 min and 72 h of reperfusion, ATP remained significantly depressed in reperfused subendocardium with values of 25 +/- 5 and 29 +/- 2 nmol/mg, respectively (P less than 0.05 and P less than 0.01 compared with the nonischemic zone in which ATP remained normal). CP levels fell during ischemia but returned to normal by 90 min of reperfusion. Percent systolic shortening of myocardial segments fell from +18 +/- 1% (active shortening) to -13 +/- 2% (passive lengthening) during ischemia and was still significantly depressed at +11 +/- 1% (P less than 0.05 vs. preocclusion) at 72 h of reperfusion. Histological examination showed no necrosis, but ultrastructural abnormalities were present. Therefore brief periods of myocardial ischemia are not associated with necrosis but result in functional, biochemical, and ultrastructural abnormalities, which are present for at lest 3 days after coronary reperfusion.