FGF21 and heart failure: Interestingly, one recent study detected that the cardiac FGF21 gene expression levels in heart failure patients were as low as healthy subjects, but the protein levels of FGF21 in both the serum and cardiac section were aberrantly increased and accompanied by elevated cardiac FGFR3 expression, which indicated the existence of a FGF21-dependent cardiohepatic signaling circuit 74.