Objectives:To explore the effect of mammalian target of rapamycin (mTOR) antagonist rapamycin (RAPA) on the imbalance of regulatory immune T cell (Treg)/regulatory immune T cell (Th17) immune homeostasis in mice with heart failure (HF) by regulating mTOR signaling pathway. Methods:The model of heart failure after myocardial infarction was constructed by ligation of the left anterior descending coronary artery in 34 healthy C57BL/6 mice.The mice were randomly divided into sham operation group,heart failure (HF) group,low-dose (1 mg/[kg·d])RAPAgroup (RAPAL group),medium-dose (2 mg/[kg·d]) RAPA group (RAPAM group) group and high-dose (4 mg/[kg·d]) RAPA group (RAPAH group) according to the random number table method,with 6 mice in each group.RAPA was administered via tail vein for 4 weeks,and the other groups were injected with the same amount of normal saline by tail vein for 4 weeks.The cardiac structure and function of mice were evaluated by echocardiography.The morphological changes of myocardial tissue were observed by hematoxylin-eosin (HE) staining.The degree of myocardial fibrosis were observed by Sirius red staining The levels of Treg and Th17 cells in peripheral blood were detected by flow cytometry.Western blot was used to detect the protein expression of mTOR,phosphorylated-mTOR (p-mTOR) in myocardial tissue. Results:Echocardiography examination revealed that compared with sham operation group,left ventricular ejection fractions (LVEF) and left ventricular short axis shortening rate (LVFS) were significantly lower ( both P<0.01),and Left ventricular end-diastolic Diameter (LVEDD) and Left ventricular end-systolic diameter (LVEDS) were significantly larger (both P<0.05) in HF group.Compared with HF group,LVEF in RAPAL group,RAPAM group and RAPAH group were significantly higher (all P<0.01),LVFS were significantly higher (all P<0.05).LVEDS in RAPAM and RAPAH groups were significantly lower than those in HF group (both P<0.05).HE staining and Sirius red staining showed that compared with the sham operation group,the myocardial tissue of the HF group was disordered,broken,and enriched with myocardial fibrosis.Compared with the HF group,the myocardial tissue disorder,breakage,and myocardial fibrosis of the RAPAL group,RAPAM group,RAPAH group were all improved.Flow cytometry and protein immunoblotting showed that compared with the sham operation group,the percentage of peripheral blood Treg cells in the HF group was decreased (P<0.01),the percentage of Th17 cells was increased (P<0.01),the Treg/Th17 ratio was decreased (P<0.01),and There was no significant difference in the expression of p-mTOR protein in myocardial tissue (P>0.05).Compared with the HF group,the percentage of peripheral blood Treg cells in the RAPAL group,RAPAM group,RAPAH group were increased (all P<0.01),the percentage of Th17 cells were decreased (all P<0.05),the ratio of Treg/Th17 in the RAPAM and RAPAH groups were all increased (P both<0.01),and the expression of p-mTOR protein in myocardial tissue were all downregulated (both P<0.01). Conclusions:Targeted inhibition of mTOR signaling can regulate the imbalance of Treg/Th17 immune homeostasis in HF mice,reduce myocardial fibrosis and improve cardiac function,among which the high-dose RAPA has the most significant effect.