Why does bystolic say not to take if you get skipped beats?

Bystolic=BetaBlocker: Beta Blockers bind to beta receptors (receptors for adrenaline & noradrenaline), at end organ level, without stimulating them. Thus reduce end organ responses to the stimulating neurotransmitters released from nerve endings from brain to end organ. They do not affect parasympathetic acetycholine receptors typically signaling opposite response. Concern=about possibly ↑ing skipping/↓ing heart rate.