Ｏｂｊｅｃｔｉｖｅ　Investigating the protective effects and expression level of the preproenkephalin(PPENK) by using Non-virus and Non-plasmids PPENK-minimalistic immunological defined gene expression(MIDGE)-nuclear localization sequence(NLS) construct on myocardial ischemia/reperfusion(I/R) injury in rats.　Methods　 Forty eight SD rats were divided into four groups randomly as(n=12): sham operation group (group C), I/R group (group I/R), gene vector group (group P), and antagonist group (group D). Group C was treated identically as other groups except left anterior descending was not tied. Group I/R was treated with 30 min of occlusion and 24 h reperfusion. Group P was given PPENK-MIDGE-NLS gene vector by tail vein injection 24 h later and then established the rat model of myocardial I/R. Group D was injected with PPENK-MIDGE-NLS gene vector from tail vein 24 h before and was injected naltrindole(1g/kg) 30 min before the rat model of myocardial ischemia reperfusion was established. Hemodynamic indexes including MAP and HR were recorded at T1(before ischemia), T2(30 min after ischemia) and T3(30 min after reperfusion).According to the Lambeth conference standard, arrhythmia situation were recorded and scored within 30 min ischemia and 30 min reperfusion. At the end of reperfusion, the level of cardiac troponin I(cTnI) in plasma was measured by ELISA Kit. Myocardial infarction size was measured by Triphenyltetrazolium Chloride. The morphology change of cardiomyocyte was observed with lens microscope, and the protein expression level of proenkephalin(PENK) in the myocardial tissue was measured by western blotting.　Results　PPENK-MIDGE-NLS gene vector could reduce the drop extents of MAP and HR that induced by myocardial I/R in rats. The expression level of cTnI in group P was reduced compared with I/R proup and group D(P＜0.05). The cardiac arrhythmia score in group P (2.0±0.9) was reduced compared with group I/R(4.1±0.6) and group D(4.0±1.0)(P＜0.05). The myocardial infarction size in group P was decreased significantly compared with group I/R(P<0.05). The morphology change of myocardial injury was reduced obviously in group P. The expression of PENK protein was increased compared with other groups(P<0.05).　Conclusions　PPENK-MIDGE-NLS gene vector transfection enhanced the expression level of proenkephalin and had a protective effect on myocardial I/R injury in rats.