Objective To examine the protective effect and mechanism of formononetin on rat cardiomyocyte injury induced by hy-poxia/reoxygenation.Methods The H9C2 rat cardiomyocytes were randomly divided into the control group,hypoxia/reoxygenation group,and formononetin group.Cells in the control group were cultured in conventional incubators,and cells in the hypoxia/reoxygenation group were cultured in hypoxia incubators and conventional incubators alternately.Cells in the formononetin group were treated with 35μmol/L formononetin after incubation in the hypoxia/reoxygenation.Cell activity was tested by a cell activity detection kit.The content of oxidative stress and inflammatory response indicators were examined by related test kits.The flow cytometry and polynucleotide chain break detection technology were used to detect apoptosis levels.Western blot was used to detect the levels of apoptosis-related proteins.Results Compared with the control group,cells in the hypoxia/reoxygenation group showed decreased cell activity and increased oxida-tive stress,inflammatory damage,and apoptosis(P＜0.05).Compared with the hypoxia/reoxygenation group,cells of the formononetin group showed increased cell activity and decreased oxidative stress,inflammatory damage,and apoptosis(P＜0.05).Conclusion For-mononetin may protect against hypoxia/reoxygenation injury by reducing the apoptosis of H9C2 rat cardiomyocytes.