Key findings of our study include: (a) the demonstration of neutrophil S100a9 lactylation and its transcriptional regulation; (b) the release of lactylated S100a9 via NETs, which triggered CM death by impairing mitochondrial function; (c) the identification of specific lactyltransferase DLAT and its inhibitor ALA; (d) the blockade of lactylation signaling driven by DLAT improved cardiac function following MI/R; (e) an independent association of S100a9K26la with cardiac death for patients with AMI following PCI. Here, S100A9 is linked to myocardial infarction.