This study aims to investigate the distribution of gut microbiota-derived metabolites, and to evaluate whether postoperative nutritional intervention can modulate the gut-heart metabolic axis, thereby improving metabolic profiles and clinical outcomes.

Background： Cardiovascular diseases remain the leading cause of mortality worldwide. Recent research has highlighted the role of gut microbiota and its metabolites-such as trimethylamine-N-oxide, phenylacetylglutamine, and p-cresyl sulfate-in the pathogenesis of cardiovascular disease through mechanisms involving inflammation, oxidative stress, and vascular dysfunction. However, little is known about the actual distribution of these metabolites in human cardiac tissues or their correlation with circulating levels. No clinical studies to date have systematically examined both tissue and blood samples in this context.

Methods： Preoperative blood samples and intraoperative cardiac tissue specimens will be collected. Both targeted and untargeted metabolomics analyses will be performed using mass spectrometry to detect key gut microbiota-derived metabolites. A subset of patients will receive postoperative probiotic supplementation. Serial blood will be collected to monitor changes in the metabolome and gut microbial composition.

Inclusion Criteria:

• Scheduled to undergo cardiovascular surgery
• Completed preoperative clinical and imaging evaluations
• Willing to provide informed consent
• Willing to receive potential probiotic supplementation

Exclusion Criteria:

• Use of antibiotics, probiotics, or other treatments affecting gut microbiota within 4 weeks
• History of major gastrointestinal disease