Abstract: OBJECTIVE To observe the relationship between the expressions of peripheral blood microRNA-21（miRNA-21）/protein tyrosine phosphatase gene（PTEN） and the myocardial injury and prognosis of chronic heart failure（CHF） patients complicated with Klebsiella pneumoniae（MP） infection. METHODS The patients with CHF who were treated in Affiliated Central Hospital of Huzhou Normal University from Jun 2019 to Jun 2021 were enrolled in the study and divided into the MP infection group with 70 cases and the non-MP infection group with 110 cases. The levels of peripheral blood miRNA-21, PTEN mRNA, serum markers of myocardial injury creatine kinase isoenzyme（CK-MB）, lactate dehydrogenase（LDH）, cardiac troponin I（cTnI）, aspartate aminotransferase（AST） were observed and compared between the two groups, the relationship between the peripheral blood miRNA-21、PTEN mRNA and the markers of myocardial injury was observed by Pearson correlation analysis. The patients of the MP infection group were divided into the poor prognosis group and the favorable prognosis group according to the major adverse cardiovascular events（MACE） within 3 months. The expression levels of peripheral blood miRNA-21 and PTEN mRNA were compared between the two groups, and the efficiencies of the indexes in prediction of poor prognosis was analyzed. RESULTS The expression levels of peripheral blood miRNA-21 and PTEN mRNA as well as the levels of serum CK-MB, LDH, cTnI and AST were higher in the MP infection group than in the non-MP infection group（P＜0.05）. Pearson correlation analysis showed that the relative expression levels of peripheral blood miRNA-21 and PTEN mRNA were positively correlated with the levels of serum CK-MB, LDH, cTnI and AST（P＜0.05）. The relative expression levels of peripheral blood miRNA-21 and PTEN mRNA of the poor prognosis group were higher than those of the favorable prognosis group（P＜0.05）. Receiver operating characteristic（ROC） curve analysis indicated that the joint detection of peripheral blood miRNA-21 and PTEN mRNA had high value in prediction of poor prognosis of the CHF patients complicated with MP infection（P＜0.05）. CONCLUSION The CHF patients complicated with MP infection show up-regulated expressions of peripheral blood miRNA-21 and PTEN mRNA, which are closely associated with the myocardial infarction, and the joint detection of the two indexes may predict the poor prognosis.