RLN2 and atrial fibrillation: Until now, only two works have reported relaxin-2 circulatory levels in patients with AF8,9, but in none of them has been described an association between relaxin-2 levels and the rhythm of the patients, except for the work of Zhou et al. (2016), which included control patients with sinus rhythm (without AF, and for this reason not comparable to our study) in which serum relaxin-2 levels were significantly lower than in both paroxysmal and persistent AF patients8.