▁and ▁bio chem istry ▁▁ β 1 - select ivity ▁▁ ▁B eta ▁block ers ▁help ▁patients ▁with ▁card i ov asc ular ▁disease ▁by ▁blocking ▁ β ▁re cept ors , ▁while ▁many ▁of ▁the ▁side - effect s ▁of ▁these ▁medic ations ▁are ▁caused ▁by ▁their ▁block ade ▁of ▁ β 2 ▁re cept ors . ▁For ▁this ▁reason , ▁beta ▁block ers ▁that ▁select ively ▁block ▁ β 1 ▁ad r ener g ic ▁re cept ors ▁( ter med ▁card io select ive ▁or ▁ β 1 - select ive ▁beta ▁block ers ) ▁produce ▁fewer ▁ad verse ▁effects ▁( for ▁instance , ▁bron cho con str iction ) ▁than ▁those ▁dru gs ▁that ▁non - select ively ▁block ▁both ▁ β 1 ▁and ▁ β 2 ▁re cept ors . ▁ ▁In ▁a ▁labor atory ▁experiment ▁conducted ▁on ▁bi ops ied ▁heart ▁t issue , ▁ne b iv ol ol ▁proved ▁to ▁be ▁the ▁most ▁ β 1 - select ive ▁of ▁the ▁ β - block ers ▁tested , ▁being ▁approximately ▁ 3 . 5 ▁times ▁more ▁ β 1 - select ive ▁than ▁bis op rol ol . ▁However , ▁the ▁drug ' s ▁re ceptor ▁select ivity ▁in ▁humans ▁is ▁more ▁complex ▁and ▁depends ▁on ▁the ▁drug ▁do se ▁and ▁the ▁gen etic ▁profile ▁of ▁the ▁patient ▁taking ▁the ▁medic ation . ▁The ▁drug ▁is ▁highly ▁card io select ive ▁at ▁ 5   m g . ▁In ▁addition , ▁at ▁dos es ▁above ▁