The beneficial effect of the DOR agonist in our study was evidenced by the reduced myocardial infarct size as shown in TTC-Evans blue staining, decreased serum levels of myocardial enzymes, decreased apoptosis of myocardial cells and decreased expression levels of caspase-3, TCF4, Wnt3a, and β-Catenin, and improved functions of the left ventricle in the mouse model of MI/R injury. The gene discussed is CASP3; the disease is myocardial infarction.