TGFB1 and atrial fibrillation: Caveolin‐1, mitogen‐activated protein kinase 4, and relaxin are negative TGFβ1 regulators that can reverse atrial fibrosis.38, 39, 40 TGFβ1 is an upstream and initiating factor with a wide range of physiological functions; and therefore, its ability to treat AF effectively is limited by its lack of specificity and side effects.