OBJECTIVE To investigate the delayed cardioprotection induced by remifentanil in intact rat ischemia-reperfusion (I/R) models. METHODS Totally 42 adult male Wistar rats weighing 200-300 g were randomly divided into 7 groups (n = 6 in each group): In Group I, rats were injected with normal saline via tail vein, performed with the regimen of 3 x 5-min intravenous (i.v.) infusion at a rate of 0.1 ml x kg(-1) min(-1) 24 h before I/R; In Group II, rats were treated according to the same experimental protocols as in Group I except receiving additional naloxone (0.1 mg/kg) 10 minutes before normal saline pretreatment; In Groups III, IV, V, and VI, rats were treated with remifentanil via tail vein, performed with the regime of 3 x 5-min i.v. infusion at a rate of 2 microg x kg(-1) x min(-1) 12 h, 24 h, 48 h, and 72 h before I/R; In Group VII, the rats were treated according to the same experimental protocols as in Group IV except that they received additional naloxone (0.1 mg/kg) 10 minutes before remifentanil pretreatment. Heart rate (HR), mean arterial pressure (MAP), and a lead II electrocardiogram were continuously monitored during IR process. To determine plasma concentration of creatine kinase myocardial isoenzyme-MB (CK-MB), arterial blood samples were obtained immediately before ischemia, and at the end of ischemia and reperfusion. After a 120-min reperfusion, heart was removed for the measurement of myocardial infarct size. Infarct size (IS) was expressed as percentage of the area at risk. RESULTS HR, MAP, and rate-pressure product were not significantly different at each time points among all groups (P > 0.05). Compared with Group I, plasma concentrations of CK-MB at the end of ischemia and reperfusion and myocardial infarct size were significantly lower in Groups IV and V (P < 0.05). Compared with Group IV, plasma concentrations of CK-MB at the end of ischemia and reperfusion were significantly higher and myocardial infarct size was significantly larger in Group VII (P < 0.05). CONCLUSIONS Remifentanil preconditioning induces delayed cardioprotection in intact rat ischemia-reperfusion model, which may be triggered via opioid receptors.