When is it dangerous to take beta blockers (25mg)? my hr goes down to 45 resting and maybey i will get dangerous rhytms?

Bradycardia: Since you are having severe bradycardia, with only 25mg, you need to discuss with your dr. as this class may not be best for you. Best wishes.

Well...: I would like to know which beta blocker are you taking, and why. But a heart rate below 60 is not a good thing

Heart meds : If your heart rate is already in the forties you certainly don't want a Beta Blocker. Talk to your doctor.... Why she wants you on BB? What is your diagnosis? What are the alternative treatment available... Please get all that info.