We found that there was relatively higher infiltration of activated CD4 T cells, activated CD8 T cells, activated dendritic cells, CD56dim natural killer cells, immature dendritic cells, MDSCs, neutrophils, plasmacytoid dendritic cells and type-2 T helper cells in the m6A cluster-C group than in the m6A cluster-A group, suggesting the essential role of m6A modification in the regulation of the immune microenvironment in AF. The gene discussed is CD8A; the disease is atrial fibrillation.