Sepsis-induced cardiomyopathy (SIC) is a rapidly progressing condition with poor prognosis in the absence of effective therapeutic interventions. Cardiomyocyte pyroptosis is a critical factor contributing to cardiac dysfunction in SIC. Currently, research on this mechanism remains unclear. We performed LPS-induced primary mouse cardiomyocyte modeling and mouse SIC modeling. Through mRNA-Seq, we found significant pyroptosis in the cardiac tissue of SIC mice. Further confocal microscopy and immunoprecipitation results confirmed that PTX3 is an important participant in cardiomyocyte pyroptosis. We then used ChIP and dual-luciferase reporter assays to confirm that SOX18 exerts a transcriptional repression effect on PTX3. M6A-Seq and RNA stability assays confirmed that the m6A modification mediated/recognized by RBM15/YTHDF2 is a crucial factor in the changes of SOX18 in SIC. Our experiments demonstrated that the abnormally elevated PTX3 in SIC plays a key role in mediating pyroptosis. Under physiological conditions, PTX3 transcription is repressed by SOX18. However, during septic cardiomyopathy, SOX18 stability is compromised by RBM15/YTHDF2-mediated m6A modification, leading to increased PTX3 levels and the subsequent induction of cardiomyocyte pyroptosis. In summary, we have delineated the RBM15/YTHDF2-SOX18-PTX3 axis in SIC. It provides a new approach for the treatment of cardiomyocyte pyroptosis in SIC and for improving prognosis.