Objective To investigate the protective effect and mechanism of magnesium isoglycyrrhizinate(MgIG)on cisplatin(CDDP)-induced myocardial injury in rats.Methods Twenty-four Wistar rats were randomly divided into the normal control group,the cisplatin model group(CDDP group),the cisplatin+magnesium isoglycyrrhizinate low-dose group(MgIG-L group)and the cisplatin+magnesium isoglycyrrhizinate high-dose group(MgIG-H group),with 6 rats in each group.Changes of body mass of rats were monitored daily.At the end of drug administration,cardiac function indexes including left ventricular ejection fraction(LVEF),left ventricular short-axis narrowing rate(LVFS),left ventricular end-systolic internal diameter(LVESD)and left ventricular end-diastolic internal diameter(LVEDD)were detected by echocardiography.The morphology of myocardial tissue was observed by HE staining.Enzyme-linked immunosorbent assay(ELISA)was used to detect serum levels of creatine kinase isoenzyme MB(CK-MB)and troponin I(cTnI).Levels of superoxide dismutase(SOD),malondialdehyde(MDA),glutathione synthase(GSH),reactive oxygen species(ROS)and ferrous ion(Fe2+)in homogenates of myocardial tissue were measured biochemically.The protein expressions of nuclear factor E2-associated factor 2(Nrf2),long-chain fatty acyl coenzyme A synthase 4(ACSL4),glutathione peroxidase 4(GPX4)and ferritin heavy chain 1(FTH1)protein were detected by Western blot assay.Results The body mass of rats in the control group showed an increasing trend during feeding,and the body mass of rats in the CDDP group showed a decreasing trend.Compared with the CDDP group,the body mass of rats in the MgIG-L group and the MgIG-H group increased after 5 d,9 d and 13 d of treatment(P＜0.05).Compared with the control group,the CDDP group showed decreased LVEF and LVFS,increased LVESD and LVEDD,disturbed myocardial fiber alignment,myocardial fiber degeneration and fracture,increased serum CK-MB and cTnI levels,increased levels of MDA,Fe2+and ROS in myocardial tissue,decreased levels of SOD and GSH,and decreased levels of Nrf2,GPX4,and decreased FTH1 protein expression levels and increased ACSL4 protein expression levels in myocardial tissue(P＜0.05).Compared with the CDDP group,the above indicators and myocardial histopathological changes were significantly improved in the MgIG-L group and the MgIG-H group.Conclusion Magnesium isoglycyrrhizinate can ameliorate cisplatin-induced myocardial injury by regulating myocardial oxidative stress and inhibiting cardiomyocyte iron death in rats.