ADRB3 and hydrops fetalis: The novel findings in this study were that 1) the occurrence frequency and the OD value of β3-AR Abs in patients with HF were much higher than that of healthy subjects, and 2) β3-AR Abs could ameliorate cardiac dysfunction in AAB rats, and its negative inotropic and chronotropic effects and inhibition of L-type calcium channels may be responsible for the protective effects.