BACKGROUND: Myocardial ischemia/reperfusion (I/R) injury is a significant complication following acute myocardial infarction (AMI) and lacks effective therapies. The involvement of gut microbiota in regulating ferroptosis during myocardial I/R injury has not been thoroughly explored. This study aimed to investigate the effect of Lactobacillus on myocardial I/R injury and explore its potential mechanisms. METHODS: One hundred fifty eight patients with ST-elevation myocardial infarction (STEMI) were enrolled in our prospective observational study. The correlations between Lactobacillus levels and myocardial injury markers, inflammatory factors, oxidative stress, and ferroptosis were evaluated. Furthermore, 30 rats were treated with Lactobacillus or vehicle control for 4 weeks, followed by myocardial I/R surgery. The protective effects of Lactobacillus against I/R injury were assessed by quantifying myocardial apoptosis, inflammation, oxidative stress, and ferroptosis. In addition, the above results were verified in vitro. The signaling pathways were investigated through the knockdown and overexpression of sirtuin 1 (Sirt1) and nuclear factor erythroid 2-related factor 2 (Nrf2). RESULTS: In clinical study, Lactobacillus levels were significantly negatively correlated with myocardial injury markers, inflammatory factors, and malondialdehyde (MDA), but positively correlated with glutathione (GSH). In rats, Lactobacillus decreased the levels of myocardial injury markers, reduced the size of the myocardial infarction area, ameliorated the disordered myocardial cell arrangement, and improved cardiac function. In both in vivo and in vitro studies, Lactobacillus inhibited cardiomyocyte apoptosis by upregulated B-cell lymphoma-2 (Bcl-2), downregulated Bcl-2 associated X (Bax), and caspase-3. Furthermore, Lactobacillus decreased inflammatory factors, MDA, reactive oxygen species (ROS) levels, and increased superoxide dismutase (SOD) activity. For ferroptosis, Lactobacillus upregulated the expression of glutathione peroxidase 4 (GPX4) and downregulated the expressions of acyl-CoA synthetase long-chain family member 4 (ACSL4) and transferrin receptor protein 1 (TfR1). Finally, knockdown and overexpression of Sirt1 and Nrf2 in vitro demonstrated that Lactobacillus exerted the effect by upregulating the Sirt1/Nrf2/HO-1 pathway. CONCLUSIONS: Our findings reveals that Lactobacillus protects against myocardial I/R injury by inhibiting apoptosis, inflammation, oxidative stress, and ferroptosis through the Sirt1/Nrf2/HO-1 signaling axis, suggesting a novel probiotic-based therapeutic potential for I/R injury.