Why do beta blockers cause bradycardia?!

I have to assume that because you're asking this you don't understand how betablockers work in the first place. You may be aware of what the desired result is but not the actual mechanism.

Betablockers are the same as beta receptor antagonists. "Betablocker" is a shorter way to say it. This class of drug interferes with the action of norepinephrine and epinephrine -- betablockers prevent these neurotransmitters, these catecholamines, from binding to beta-receptors on neurons. There are 3 kinds of beta-receptors -- Beta-1, beta-2 and beta-3. These receptors are if different locations in the body according to the functions they control. Beta-1 receptors are found in heart, kidney and eye tissue and because you're asking about bradycardia, beta-1 receptors are probably the ones in question but beta-2s could just as well be included.

So not all betablockers affect the heart exclusively. Therefore, your question could read "Why do some betablockers cause sinus bradycardia?". But they don't always cause sinus bradycardia. It's that there is a potential for this.

You may already know (or have guessed) that the catecholemines, epinephrine and norepinephrine, accelerate heart rate but also stimulate it. Fight or flight, remember? Beta-1 bockers attach to beta-1 receptors, thus blocking neurotransmitters from doing so. Result? Lowered heart rate. There is a risk for bradycardia with calcium channel blockers, betablockers, alpha/beta-adrenergic blockers and digoxin.

The precise mechanism is as follows: A medication such as metoprolol or atenolol, decrease heart rate and myocardial contractility by blocking epinephrine stimulation at beta-receptor sites to decrease myocardial oxygen consumption and the hearts workload. Betablockers can be cardioselective or nonselective. Cardioselective agents block beta-receptors only in the heart; and nonselective agents beta-receptors in the heart, lungs, and vascular smooth muscle.

Not all betablockers target cardiac neurons and it's not a foregone conclusion that some one taking a betablocker will become bradycardic. There is a risk, a potential, for bradycardia and not a certain guarantee. I wish to make this very clear.

I'm a nurse.

thats intresting i never heard of bradycardia only tachycardia- which i have. i google your word and see that its a slow heart rate. well i used to take beta blockers but stopped for some reasons.. but i know that when i was on beta blockers my heart rate never went that slow