At the molecular level, myocardial β-AR dysfunction in HF is characterized by loss of β1-AR density (around 50%) at the plasma membrane (downregulation) and by uncoupling of the membrane β1-ARs and β2-ARs from G proteins (desensitization) (Bristow et al., 1986; Ungerer et al., 1993) (Figure 2). The gene discussed is ADRB2; the disease is hydrops fetalis.