When EC acts as a signal sender, we found that EC autocrine signals—VEGF–VEGFR, EFNB/A1–EPHB4, JAM–F11R/JAM, APP–CD74, and ANGPT–TEK—and secretory signals to APF (e.g., GRN–SORT1, AGRN–DAG1, JAG2/DLL1–NOTCH3) were missing in AF. Here, DLL1 is linked to atrial fibrillation.