BACKGROUND: Some opioids have been shown to attenuate an ischemia-reperfusion injury in an isolated-heart model. The aim of this study was to evaluate the effect of sufentanil on the cardiac function in isolated-heart models when given before and after prolonged periods of low flow ischemia. METHODS: Isolated rat hearts were stabilized for 30 minutes and subdivided into four groups (each n = 7). The control group was subjected to low flow ischemia (LFI 0.3 ml/min) of 5% dextrose water for 30 minutes, followed by perfusion with a modified Krebs solution at a constant pressure for 60 minutes. In the sufentanil groups, different sufentanil (12.5 mg/L, 25 mg/L, 50 mg/L) doses were administered with the modified Krebs solution after 30 minutes of stabilization until the end of the experiment with the exception of the LFI group. The left ventricular end systolic pressure (LVESP), dP/dt max, heart rate and coronary flow were measured. After reperfusion, the infarct size of all groups was measured. RESULTS: The control and the sufentanil groups had a lower LVESP, dP/dt max, coronary effluent flow and arrhythmia duration after ischemia and reperfusion than those before ischemia. The infarct sizes in the sufentanil groups were smaller than those in the control group. However the infarct sizes of the sufentanil groups were similar. CONCLUSION: Sufentanil reduces the infarct size but does not improve the post-ischemic functional dysfunction.