ADRB1 and heart failure: Selective β2-AR (but not β1) blockade has been found to be highly antiarrhythmic in heart failure due to a reduction of sarcoplasmatic reticulum calcium load [57] and the beta blocker Metoprolol that has recently shown a higher affinity to β2-AR than to β1-AR [58] has been effectively administered to treat arrhythmias.