Consistent with diminished arrhythmogenic substrate(s) in Dsg2mut/mut × Ccr2–/– and Dsg2mut/mut × IκBαΔN mice, infusion of dobutamine (a β1-adrenergic agonist) and caffeine at 16 weeks of age resulted in fewer induced arrhythmias compared with Dsg2mut/mut mice (Supplemental Figure 4). This evidence concerns the gene CCR2 and cardiac arrhythmia.