Why when andrenergic blockers decrease the sympathetic nervous system do they cause tachycardia?

Answer:
they don't- adrenergic blockers (commonly called beta blockers) would all cause bradycardia. stimulation of the beta-1 receptor would cause an increase in heart rate. blocking that receptor, which is what you would do with a beta blocker, would therefore cause a decrease in heart rate.

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Alpha adrenergic blockers cause a reflex tachycardia. I answered your question when you asked it again.

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