BACKGROUND: The relationship between aging, gut microbiota, and cardiac repair after myocardial infarction (MI) remains unclear. Understanding this interaction may provide novel strategies for improving cardiovascular outcomes in the elderly. METHODS: Aged mice were treated with antibiotics followed by fecal microbiota transplantation (FMT) from young or aged donors prior to MI. Cardiac function, gut integrity, immune signaling, and metabolism were evaluated. Gut microbiota and plasma metabolites were also profiled in ST-elevation myocardial infarction (STEMI) patients across age groups. RESULTS: Young FMT improved post-MI cardiac function and reduced infarct size in aged mice. It preserved intestinal barrier integrity, reduced IL-17A-positive immune cells, and attenuated age-related intestinal shortening. Aging was associated with decreased microbial diversity, loss of beneficial taxa such as , and enrichment of inflammatory pathways. Cardiac metabolomics revealed reduced oxidative metabolism and increased lipid reliance in aged mice. In STEMI patients, aging correlated with lower microbiota diversity, altered taxonomic profiles, and shifts in lipid and amino acid metabolism. CONCLUSIONS: This study highlights the role of gut microbiota in cardiovascular health and aging. Microbiota transplantation improved cardiac recovery, suggesting its therapeutic potential and offering new insights into the gut-heart axis for future treatments in age-related cardiovascular disease.