Objective: To investigate the effect of potassium channel opener nicorandil on myocardial ischemia-reperfusion injury (MIRI) in isolated rat's heart. Methods: Langendorff system was established for isolated heart reperfusion. A total of 44 rats were randomly divided into 4 groups: Normal control group, Ischemia-reperfusion (I-R) group, Adenosine/I-R (A/I-R) group, the I-R heart was treated by adenosine 100 μmo/L and Nicorandil/I-R (N/I-R) group, the I-R heart was treated by nicorandil 200 μmo/L.n=11 in each group. Left ventricular developed pressure (LVDP), the maximal rise/fall rate of left ventricular pressure (±dp/dtmax), reperfusion arrhythmia (RA) and myocardial infarction (MI) size were recorded; the expressions of left ventricular tissue acetaldehyde dehydrogenase 2 (ALDH2), Bcl-2 and Bax were examined and compared among different groups. Results:①Compared with I-R and A/I-R groups, N/I-R group had increased LVDP at 30 min and 45 min reperfusion, allP<0.05.②Compared with N/I-R and A/I-R groups, I-R group showed reduced ±dp/dtmax at 30 min and 45 min reperfusion, allP<0.05; while ±dp/dtmax in N/I-R group was higher than A/I-R group at 30 min and 45 min reperfusion, all P<0.05.③Compared with I-R group, both N/I-R and A/I-R groups presented reduced RA score, allP<0.01, RA score was similar between N/I-R group and A/I-R group,P=0.771.④compared with I-R group, both N/I-R and A/I-R groups had the smaller MI size,P<0.01 and N/I-R group showed the smaller MI size,P<0.05.⑤Compared with Normal control group, I-R group had decreased mitochondrial ALDH2 expression and increased Bcl-2, Bax expression; ALDH2 level was elevated in N/I-R group had reduced in A/I-R group; Bcl-2 and Bax levels were increased in both N/I-R and A/I-R groups. Compared with I-R group, both N/I-R and A/I-R groups had increased ratio of Bcl-2/Bax,P<0.05; the anti-apoptosis effect was similar between N/I-R group and A/I-R group,P>0.05. Conclusion: Nicorandil may reduce MIRI and protect myocardium in isolated rat's heart, the overall effect is better than adenosine. Nicorandil can up-regulate the expressions of mitochondrial ALDH2, Bcl-2 and down-regulate the expression of Bax.