In patients with mild HF, elevated serum FGF21 levels were significantly correlated with decreased NT-proBNP levels (ρ = −0.37, p = 0.0022), E/e’ ratio (ρ = −0.29, p = 0.0182), TR velocity (ρ = −0.24, p = 0.0470) and RV-RA gradient (ρ = −0.24, p = 0.0472). This evidence concerns the gene FGF21 and hydrops fetalis.