〔Abstract〕 Objective To study whether intestinal bacterial microenvironment and its metabolites are involved in the occurrence and development of heart failure in rats.Methods The heart failure model of rats was induced by subcutaneous injection of isoproterenol, and the success of the model was evaluated by echocardiography after feeding for one and a half months, and then the rats were divided into two groups: heart failure(HF) group and control group. The serum TMAO level of rats was determined by high performance liquid chromatography tandem mass spectrometry. Fecal samples of the control group and HF group were collected for bacterial DNA extraction,and then conducted 16 SrDNA high-throughput sequencing. The diversity,relative abundance and different species of intestinal flora were analyzed using the NovoMagic cloud platform.Results Compared with the control group,serum TMAO level in HF group significantly increased(P<0. 05). Sequencing results of fecal samples in the two groups showed that at the phylum level,the top three bacteria were Firmicutes,Bacteroidetes and Actinobacteria. At the genus level,the top three species were Lactobacillus,Allobaculum and Duchella. The diversity analysis of the two groups showed that the structure of intestinal flora in HF group was similar to that in control group. The analysis of species differences with the T test showed that the top five bacteria groups with differences between the two groups were Acidobacteriota,Verrucomicrobiota,Nitrospirota,Methylomirabilota and Crenarchaeota(P<0. 05). There was no significant difference in the comparison of other flora(P>0. 05). LEFSE analysis showed that Lactobacillus murinus,Acidobacteriota,Bacteria had significant differences between HF group and control group(LDA absolute value>4).Conclusion The changes of intestinal flora and its metabolites TMAO levels are involved in the occurrence and development of heart failure in rats.