ObjectiveTo observe the effects of astragaloside Ⅳ （AS-Ⅳ） and tanshinone Ⅱ_A （Tan Ⅱ_A） in antagonizing adverse cardiac remodeling after myocardial infarction （MI） and to explore the mechanism by which they regulate myocardial copper homeostasis to improve the mitochondrial function. MethodsA total of 70 C57BL/6J mice were randomly assigned into a sham-operation group and a modeling group. The MI model was established by ligation of the left anterior descending coronary artery in mice. Successfully modeled mice were assigned into model （MI）， AS-Ⅳ （2 mg·kg^-1·d^-1）， Tan Ⅱ_A （15 mg·kg^-1·d^-1）， and AS-Ⅳ+Tan Ⅱ_A （2 mg·kg^-1·d^-1 AS-Ⅳ+15 mg·kg^-1·d^-1 Tan Ⅱ_A） groups. In the sham operation group， the left anterior descending artery was passed with a suture but not ligated. After 4 weeks of drug intervention， the cardiac function was assessed by echocardiography. Wheat germ agglutinin （WGA） staining and Masson staining were adopted to evaluate myocardial hypertrophy and fibrosis， respectively. Cardiac copper content was measured by colorimetry. The protein levels of copper transporter 1 （CTR1）， ATPase copper transporting alpha （ATP7A）， ATPase copper transporting beta （ATP7B）， copper metabolism domain containing 1 （COMMD1）， cytochrome C oxidase copper chaperone COX17 （COX17）， and cytochrome C oxidase subunit Ⅳ isoform 1 （COXⅣ） were determined by Western blot. In the cell experiments， a cardiomyocyte oxygen-glucose deprivation （OGD） model was established， and cells were allocated into normal， OGD， AS-Ⅳ （51 µmol·L^-1）， Tan Ⅱ_A （1.7 µmol·L^-1）， and AS-Ⅳ+Tan Ⅱ_A （51 µmol·L^-1 AS-Ⅳ+1.7 µmol·L^-1 Tan Ⅱ_A） groups. Intracellular copper content was measured by colorimetry， and reactive oxygen species （ROS） production was detected through the ROS fluorescent probe. Mitochondrial morphology and function were assessed by Mito-Tracker Red and JC-1 probes， respectively. ATP content was measured by colorimetry， and the protein levels of CTR1， ATP7A， ATP7B， COMMD1， COX17， and COXⅣ were determined by Western blot. COMMD1 levels were examined by immunofluorescence staining. ResultsCompared with the sham operation group， the model group showed decreased left ventricular ejection fraction （LVEF） and left ventricular fractional shortening （LVFS） （P<0.01）， increased cardiomyocyte hypertrophy and collagen blue staining （P<0.01）， a declined copper ion level in the cardiac tissue （P<0.01）， upregulated protein levels of ATP7A， ATP7B， and COMMD1 （P<0.01）， downregulated protein levels of COX17 and COXⅣ （P<0.01）， and no significant change in CTR1 protein level. Compared with the model group， the AS-Ⅳ， Tan Ⅱ_A， and AS-Ⅳ+Tan ⅡA groups exhibited increased LVEF and LVFS （P<0.01）， reduced cardiomyocyte hypertrophy and collagen blue staining （P<0.01）， elevated copper ion levels in the cardiac tissue （P<0.01）， and recovered protein expression （P<0.01）. The cell experimental results showed that compared with the control group， the model group exhibited decreases in intracellular copper ion level， mitochondrial membrane potential， and ATP content （P<0.01）， an increase in ROS level （P<0.01）， upregulation in the protein levels of CTR1， ATP7A， ATP7B， and COMMD1 （P<0.01）， and downregulation in the protein levels of COX17 and COXⅣ （P<0.01）. Compared with the model group， the AS-Ⅳ， Tan Ⅱ_A， and AS-Ⅳ+Tan Ⅱ_A groups showed increased intracellular copper ion levels， mitochondrial membrane potential， and ATP content （P<0.01）， decreased ROS levels （P<0.01）， and recovered protein expression （P<0.01）. ConclusionThe combination of AS-Ⅳ and Tan Ⅱ_A can alleviate myocardial fibrosis and hypertrophy after MI by restoring myocardial copper homeostasis and subsequently improving the mitochondrial function.