Aim To determine the content of apelin in acute myocardial ischemia and probe the protective mechanism of exogenous apelin-13 on myocardium ischemic injury in rats. Methods The content of apelin in myocardium and plasma was detected by enzyme linked immunosorbent assay (ELISA) in SD rats suffered from myocardial ischemia by ligating the left anterior descending coronary artery (LAD) for 30, 60 and 120 min respectively. Then the rats were randomly divided into sham operated group, model control group and two apelin-13 groups, to which apelin-13 of 10 and 100 μg/kg was infused via caudal vein 5 min before a 120 min-myocardial ischemia. The cardial function was measured by electrophysiolograph. Cardiomyocyte apoptosis was detected with TUNEL and Bcl-2, Bax and Caspase-3 protein expression of myocardium with Western blotting. Results The content of apelin in myocardium was markedly increased during myocardial ischemia 30 to 60 min and decreased to below basal level on ischemia 120 min (P<0.01). The content of apelin in plasma increased gradually during myocardial ischemia 30 to 120 min (P<0.01). In myocardial ischemia models induced by ligating LAD for 120 min, apelin-13 (100 μg/kg) infused pre-ischemia can significantly improve cardial function, inhibit the cardiomyocyte apoptosis (P<0.01), increase Bcl-2 protein expression and decrease Bax and Caspase-3 protein expression. Conclusion The content of apelin in myocardium was increased in a compensatory role in early myocardial ischemia and decreased in sustained myocardial ischemia. The protective mechanism of exogenous apelin-13 on ischemic myocardium may be related to inhibition of cardiomyocyte apoptosis.