To determine the protective effect of Apelin-13 on cardiac hypertrophy through activating the PI3K-AKT-mTOR signaling pathway. The phenylephrine-induced cardiomyocyte hypertrophy model was established in H9C2 cells in vitro. Electroporation transfection technology was utilized to prepare and screen the H9C2 cells inducing low expression of the angiotensin type one receptor-related protein (Si-APJ). H9C2 and Si-APJ cells were divided independently into five groups: the control group, the PE group, the PE+Apelin group, the PE+Rapa group, and the PE+Apelin+Rapa group. RT-PCR was performed to analyze the mRNA expression levels of myosin heavy chain 7 (MYH7). Expression of the PI3K/AKT/mTOR pathway proteins and MYH7 was investigated by western blot. The expression of PI3K/AKT/mTOR phosphorylated proteins was significantly higher in the PE group compared with the PE+Apelin group in H9C2 cells (P<0.05). Conversely, in Si-APJ H9C2 cells, the expression of PI3K/AKT/mTOR phosphorylated proteins was decreased (P<0.05). In H9C2 cells, the expression of MYH7 protein was increased in the PE group compared with the control group (P<0.05). In the same cell line, the expression of MYH7 in the PE+Apelin group was decreased significantly compared with the PE group (P<0.05). In Si-APJ H9C2 cells, compared with the control group, the expression of MYH7 in the PE group still increased significantly (P<0.05). In contrast, in the same cell line, there was no statistically significant difference in MYH7 expression between the PE+Apelin, PE+Rapa, and PE+Apelin+Rapa groups compared to the PE group (P>0.05). Apelin-13 reduces PE-induced cardiac hypertrophy by activating the PI3K/AKT/mTOR signaling pathway.