Objective: Extensive studies have shown that ERS may be implicated in the pathogenesis of DCM. We explored the therapeutic effects of lncRNAH19 on DCM and its effect on ERS-associated cardiomyocyte apoptosis. Methods: C57/BL-6j mice were randomly divided into 3 groups: non-DM group (controls), DM group (DCM), and lncRNAH19 overexpression group (DCM+H19 group). The effect of H19 on cardiac function was detected. The effect of H19 on cardiomyocyte apoptosis and cardiac fibrosis in DM was examined. Differentially expressed genes (DEGs) and activated pathways were examined by bioinformatics analysis. STRING database was applied to construct a PPI network using Cytoscape software. The expression of p-PERK, p-IRE1, ATF6, CHOP, cleaved caspase-3, -9, -12 and BAX proteins in cardiac tissue was used to determine the ERS-associated apoptotic indicators. We established the HG-stimulated inflammatory cell model. The expression of p-PERK and CHOP in HL-1 cells following HG was determined by immunofluorescence labeling. The effects of H19 on ERS and PI3K/AKT/mTOR pathway were also detected. Results: H19 improved left ventricular dysfunction in DM. H19 could reduce cardiomyocytes apoptosis and improve fibrosis in vivo. H19 could reduce the expression of p-PERK, p-IRE1 alpha, ATF6, CHOP, cleaved caspase-3, cleaved caspase-9, cleaved caspase-12, and BAX proteins in cardiac tissues. Furthermore, H19 repressed oxidative stress, ERS and apoptosis in vitro. Moreover, the effect of H19 on ERS-associated apoptosis might be rescued by LY294002 (the specific inhibitor for PI3K and AKT). Conclusion: H19 attenuates DCM in DM and ROS, ERS-induced cardiomyocyte apoptosis, which is associated with the activation of PI3K/AKT/mTOR signaling pathway.