Moreover, in contrast to the downregulation of β1- and β2-AR during the development of HF [22], β3-AR proteins were markedly increased (2- to 3- fold) in failing compared with non-failing hearts, and a similar increase was also observed for Gi proteins that coupled β3-AR to their negative inotropic effect [23-26]. Here, ADRB3 is linked to hydrops fetalis.