BACKGROUND: Fentanyl is commonly used as a anesthetics for patients who have poor cardiac reserve, because it provides cardiovascular stability. But little data exist on the effects of fentanyl on myocardial ischemia and reperfusion injury. The purpose of this study was to examine the effects of the fentanyl on the recovery of myocardial contracility, coronary flow, and myocardial oxygen balance in isolated rat hearts subjected to ischemia and reperfusion. METHODS: Isolated Sprague-Dawley rat hearts were perfused at constant pressure with oxygenated modified-Krebs solution (pH 7.4, 37oC). After stabilization period, all hearts were given fentanyl 0, 1, 10 ng/ml, respectively. Then, myocardial ischemia was induced by global ischemia for 15 minutes. Isovolumetric left ventricular pressure (LVP) and dP/dt were measured via a latex balloon and transducer. Also, coronary flow and oxygen tensions at the coronary inflow and outflow were measured. RESULTS: The application of fentanyl did not significantly affect myocardial contractility, coronary flow, and myocardial oxygen balance. After global ischemia, myocardial contractility, coronary flow, and myocardial O2 consumption were decreased, but percentage of O2 extraction was increased. However, these changes were not significantly different between fentanyl pretreated and control groups. CONCLUSIONS: These in vitro findings demonstrate that the pretreatment of fentanyl is devoid of major effects on recovery of the myocardial contracility, coronary flow, and myocardial oxygen balance in isolated stunned rat hearts.