Sepsis-induced cardiac dysfunction represents a main cause of death in intensive care units. Previous studies have indicated that GSK-3β is involved in the modulation of sepsis. However, the signalling details of GSK-3β regulation in endotoxin lipopolysaccharide (LPS)-induced septic myocardial dysfunction are still unclear. Here, based on the rat septic myocardial injury model, we found that LPS could induce GSK-3β phosphorylation at its active site (Y216) and up-regulate FOXO3A level in primary cardiomyocytes. The FOXO3A expression was significantly reduced by GSK-3β inhibitors and further reversed through β-catenin knock-down. This pharmacological inhibition of GSK-3β attenuated the LPS-induced cell injury via mediating β-catenin signalling, which could be abolished by FOXO3A activation. In vivo, GSK-3β suppression consistently improved cardiac function and relieved heart injury induced by LPS. In addition, the increase in inflammatory cytokines in LPS-induced model was also blocked by inhibition of GSK-3β, which curbed both ERK and NF-κB pathways, and suppressed cardiomyocyte apoptosis via activating the AMP-activated protein kinase (AMPK). Our results demonstrate that GSK-3β inhibition attenuates myocardial injury induced by endotoxin that mediates the activation of FOXO3A, which suggests a potential target for the therapy of septic cardiac dysfunction.