ADRB1 and cardiac arrhythmia: Pharmacological stimulation of cardiac β1AR results in indirect stimulation of cardiac A1R, through the conversion of cAMP into ADO in the extracellular medium, which in turn promotes activation of these A1R. These are responsible, in part, for the cardioprotective mechanisms that so reduce the incidence of severe CIR-induced cardiac arrhythmias responsible for death in PD model animals.