ADCY6 and hydrops fetalis: During HF, one of the most profound cellular changes is an increase in systolic Ca2+ levels and prolongation of the Ca2+ transient during diastole, leading to defects in EC coupling, cardiac dysfunction, and HF.50 EC coupling is regulated by many pathways, including β-adrenergic signalling which, when activated by β-receptor agonists, initiates the production of cAMP by Adcy6.