It has been found that atrial fibrosis is associated with the occurrence of arrhythmias and the formation of atrial fibrosis results from excessive proliferation of a-SMA-labeled myofibroblasts and excessive deposition of extracellular matrix components, including type I collagen and TGF-β1 [39–41]. The gene discussed is TGFB1; the disease is cardiac arrhythmia.