BACKGROUND: Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide. Much effort was spent to identify biomarkers useful to stratify AF patients. Mediator complex (MED) is an ancestral regulator of transcriptional mechanisms. Here, we investigated the role of methyl DNA-MED regulatory networks in AF patients. METHODS: We analyzed the methylome of circulating CD4 RESULTS: We identified 10 differentially methylated regions (DMRs) which were hypermethylated and annotated to 10 genes encoding for MED complex subunits in CD4 CONCLUSIONS: For the first time, we showed that DNA methylation changes are associated with regulation of MED complex subunits in early diagnosis of AF patients. Clinically, MED1 and MED23 hypermethylation showed a diagnostic value not inferior to circulating levels of NT-proBNP suggesting early diagnostic biomarker pathogenic molecular routes underlying disease onset.