【Abstract】 Objective To measure the roles of fibroblast growth factor 21 (FGF21) on hypoxia/reoxygenation (H/R)treated cardiomyocytes and the potential mechanisms. Methods Adenoviral vector encoding FGF21 (AdFGF21) was used to elevate FGF21 in cultured neonatal rat cardiomyocytes. The experiments were assigned into four groups: control group, H/R group, H/R+AdGFP group and H/R+ AdFGF21 group. Three hours of hypoxia and 3h of reoxygenation were performed to cause H/R injury followed after viral transfection. Cell viability was detected by CCK8 assay. The apoptosis, ROS and molecular alternations were systematically estimated. Moreover, the specific PI3K/AKT inhibitor (LY294002) was added in mechanistic detections. Results In comparison with the control group, H/R resulted in the downregulation of FGF21 followed by the worsened cardiomyocytes damage, as exhibited by the decrease of viability and the promotion of ROS and apoptosis. However, above parameters induced by H/R were attenuated by FGF21 overexpression. Mechanistic experiments showed that FGF21 elevation enhanced the levels of pPI3K/AKT, and blocking PI3K/AKT with its specific inhibitor LY294002 dampened the H/Rlimited effects of FGF21. Conclusion FGF21 ameliorates myocardial H/R injury in part via a PI3K/AKTdependent way.