Recent studies have revealed that exercise has myocardial protective effects, but the exact mechanism remains unclear. Studies have increasingly found that peptides play a protective role in myocardial ischaemia-reperfusion (I/R) injury. However, little is known about the role of exercise-induced peptides in myocardial I/R injury. To elucidate the effect of exercise-induced peptide EIP-22 in myocardial I/R injury, we first determined the effect of EIP-22 on hypoxia/reperfusion (H/R)- or H2O2-induced injury via assessing cell viability and lactate dehydrogenase (LDH) level. In addition, reactive oxygen species (ROS) accumulation and mitochondrial membrane potential (MMP) was assessed by fluorescence microscope. Meanwhile, Western blot and TUNEL methods were used to detect apoptosis level. Then, we conducted mice I/R injury model and verified the effect of EIP-22 by measuring cardiac function, evaluating heart pathology and detecting serum LDH, CK-MB and cTnI level. Finally, the main signalling pathway was analysed by RNA-seq. In vitro, EIP-22 treatment significantly improved cells viabilities and MMP and attenuated the LDH, ROS and apoptosis level. In vivo, EIP-22 distinctly improved cardiac function, ameliorated myocardial infarction area and fibrosis and decreased serum LDH, CK-MB and cTnI level. Mechanistically, JAK/STAT signalling pathway was focussed by RNA-seq and we confirmed that EIP-22 up-regulated the expression of p-JAK2 and p-STAT3. Moreover, AG490, a selective inhibitor of JAK2/STAT3, eliminated the protective roles of EIP-22. The results uncovered that exercise-induced peptide EIP-22 protected cardiomyocytes from myocardial I/R injury via activating JAK2/STAT3 signalling pathway and might be a new candidate molecule for the treatment of myocardial I/R injury.