Background <p>Atrial fibrillation (AF) is closely related to aging and involves energy metabolism remodeling. However, the changes in atrial energy metabolism associated with aging-related AF remain unclear.</p> Methods <p>Left atrial appendage samples from AF patients were analyzed for nicotinamide adenine dinucleotide (NAD_total) levels using WST-8 method, adenosine triphosphate (ATP) content with an ATP detection kit, and silent information regulator sirtuin 1 (SIRT1) expression and protein acetylation levels via western blotting. Aged canine and mouse AF models were created through rapid atrial pacing and intravenous calcium chloride and acetylcholine administration, respectively. An aged cellular AF model was developed using electrical stimulation. Atria or cells from these models were analyzed for the aforementioned parameters. Co-immunoprecipitation in 293T cells verified the interaction between histone arginine methyltransferase 1 (CARM1) and circadian rhythm output cycle protein kaput (CLOCK), and rescue experiments with CARM1 and nicotinamide phosphoribosyl transferase (NAMPT) inhibitors explored their roles in regulating NAD⁺ and atrial energy metabolism remodeling in AF.</p> Results <p>Clinical samples showed decreased NAD_total, SIRT1 and ATP levels, validated in aged canine, mouse, and cellular AF models. Cell-level tests revealed that the NAMPT activator P7C3-A20 increased NAD⁺ levels, while the inhibitor FK866 decreased them. Co-IP experiments indicated an interaction between CARM1 and CLOCK, with CARM1 expression upregulated in AF. Rescue experiments demonstrated that combined CARM1 and NAMPT inhibitors lowered NAD⁺ levels, suggesting that CARM1 regulates the CLOCK/NAMPT pathway, affecting NAD⁺ metabolism in AF.</p> Conclusions <p>CARM1 may influence the CLOCK/NAMPT pathway and may be associated with reduced NAD_total evels, potentially contributing to impaired atrial energy metabolism in aging-related AF.</p>