Specifically, ESTIMATE analysis showed that both the immune and ESTIMATE scores were higher in AF group, and Xcell analysis further demonstrated that basophils, CD8+ naïve T cells, Th1/2, Treg, dendritic cells, M2 macrophages, mast cells, monocytes, neutrophils, megakaryocytes, natural killer (NK) cells, and NK-T cells tended to infiltrate the atrial tissues of patients with AF compared to those of individuals with SR. This evidence concerns the gene CD8A and atrial fibrillation.