RLN2 and atrial fibrillation: Although only a limited number of reviews have addressed the effect of relaxin-2 in AF despite the numerous anti-fibrotic, anti-inflammatory, and anti-oxidant properties of this endogenous peptide at a cardiac level and its cardioprotective role demonstrated in preclinical models of AF and arrhythmic backgrounds [111,112,113,115,116,117], it is extremely relevant to highlight the role of relaxin-2 as a promising biomarker in AF.