The TGFB1 gene was analyzed as a candidate gene for AF because of its functional relation with the modulation of tissue fibrosis, upregulated expression in experimental and human AF [7–11,15,37], as well as selective atrial fibrosis and increased AF inducibility in cardiac-specific overexpression of constitutively active TGFB1 in mice [12–14]. The gene discussed is TGFB1; the disease is atrial fibrillation.