Objective To explore the role of serine/threonine protein kinase 4 (mammalian STE20-like protein kinase 4, MST4) in myocardial infarction (MI) and the underlying molecular mechanisms. Methods Western blot was performed to assess MST4 expression in peripheral blood mononuclear cells (PBMCs) from four MI patients and four healthy controls. Immunofluorescence staining was used to compare the co-expression of MST4 and macrophages in ischemic regions and non-ischemic regions in myocardial tissues from MI patients. The mouse models of MI were established and divided into an MST4 functional inhibition (treated with Hesperadin) group and a control group ( 12 mice in each group), and cardiac function of model was evaluated by echocardiography; Masson’s trichrome staining was employed to assess cardiac collagen deposition post-MI, and peripheral blood N-terminal pro-brain natriuretic peptide (NT-proBNP) level was measured using ELISA. Further, MST4-inhibited bone marrow-derived macrophages (BMDMs) were constructed in vitro, and immunofluorescence was used to detect the expression of the reparative macrophage marker arginase 1 (Arg1), and RT-qPCR was employed to examine changes in the expression of genes associated with reparative macrophages. Western blot analysis was performed to evaluate the activation status of mitogen-activated protein kinase (MAPK) pathway-related proteins. Results MST4 expression was significantly increased in PBMCs from patients with MI and co-localized with CD68⁺ macrophages in ischemic cardiomyopathy tissues (P＜0.000 1). In the mouse models of MI, compared with control group, Hesperadin group had increased left ventricular ejection fraction (P＜0.05), lower peripheral blood NT-proBNP level (P＜0.000 1), and did not alter total F4/80⁺ macrophage abundance. In vitro, MST4 inhibition promoted reparative macrophage-associated gene expression and suppressed protein phosphorylation in MAPK pathway (P＜0.05). Conclusions Inhibition of MST4 promotes macrophage polarization toward a reparative phenotype through modulation of MAPK pathway, thereby improving post-MI cardiac remodeling and outcome.