Apelin is the endogenous ligand of the G protein-coupled receptor, APJ. Recently, researches indicate that the apelin/APJ system involves in myocardial ischemia-reperfusion injury (MIRI), which is a common pathophysiological process in patients with heart diseases and therapies. The reperfusion induces the expression of apelin and APJ receptor, which play an important role in cardioprotection of MIRI. The apelin/APJ system alleviates MIRI mainly by decreasing mitochondrial reactive oxygen species and delaying the opening of mitochondrial permea...