Given that certain types of AAbs isolated from patients with DCM can induce a negative inotropy and reduction in calcium transients in vitro and ex vivo and that patients with cardio-depressant AAbs showed an acute improvement in cardiac function after IA therapy [110,111,112], the above mentioned more favorable outcomes of IgG3-β1AR-AAb-positive HF patients in comparison with those without evidence β1AR-AAbs suggest the existence of an important relationship between β-blockers and IgG3-β1AR-AAbs. This evidence concerns the gene IGHG3 and hydrops fetalis.