What is a dangerously low heart rate? why not everyone take Atenolol like a vitamin?

I take Atenelol for SVT (supraventricular tachycardia). You cant just pop this medication like a daily vitamin. You are only supposed to take it if you have a reason to. Im on Atenelol and my heart rate now ranges from 55-100. Anywhere in this range is perfectly safe. But make sure that you are taking this medicine for a reason and that it is prescribed by your doctor.