AR and atrial fibrillation: Studies with bucindolol, in development for the indications of chronic HF and atrial fibrillation, have demonstrated response variability dependent on two coding AR polymorphisms that affect signaling: an amino acid position 389 Arg→Gly of the cardiac myocyte located β1 AR resulting from a nucleotide position c.1165 C→G in the ADRB1 gene [11]; and a position 322–325 four amino acid deletion (Del) in the cardiac prejunctional sympathetic nerve terminal α2C AR resulting from a nucleotide position c.964–975 Del in the ADRA2C gene [12].