This increase in relaxin-2 plasma levels seems to be based on NYHA (New York Heart Association) class functional classification [98,99], and it is confirmed that relaxin-2 plasma levels and relaxin-2 gene expression in the myocardium are equivalent to the severity of HF [70], which prompted the use of endogenous relaxin-2 for a preliminary assessment of CHF severity and prognosis of the disease. The gene discussed is RLN2; the disease is hydrops fetalis.