<p>Myocardial infarction (MI) and ischemia-reperfusion injury (IRI) are critical challenges in clinical practice. The function of macrophage in this process has gained increasing attention. Macrophage polarization from pro-inflammatory (M1) to reparative (M2) phenotypes is crucial for cardiac repair. However, the regulatory mechanisms behind macrophage polarization, particularly involving m6A modification are not well understood. We utilized a mouse model of myocardial IRI to study m6A modifications and related enzymes in a mouse model of myocardial IRI. We co-cultured bone marrow-derived macrophages with conditioned medium from HL-1 cells to assess the role of FTO in macrophage polarization. Through bioinformatics analysis and m6A methylated RNA immunoprecipitation (MeRIP), <i>TRIM21</i> was identified as a target gene of FTO. Finally, we investigated the effects of FTO and TRIM21 on myocardial injury in macrophages using transgenic mice. After IRI, FTO expression was reduced in cardiac macrophages, which was associated with enhanced m6A modification and a shift toward M1 polarization. Overexpression of FTO promotes M2 polarization, reduces inflammatory cytokine levels, and attenuates myocardial injury. In addition, TRIM21 knockdown inhibited activation of the NF-κB pathway, thereby suppressing M1 polarization. In vivo experiments using transgenic mice expressing FTO and TRIM21 specifically in macrophages demonstrated that FTO attenuated myocardial injury, whereas TRIM21 exacerbated myocardial injury through an opposite effect on macrophage polarization. These findings emphasize the critical roles of FTO and TRIM21 in macrophage-mediated myocardial repair and provide potential therapeutic targets for attenuating IRI.</p>