Is bradycardia an arrhythmia?

Yes: Bradycardia is a term to describe a heart rate that is abnormally low. There are many situations where bradycardia, while technically an arrhythmia, is not a concern. Individuals who exercise frequently, particularly endurance athletes such as cyclists and distance runners, typically have low heart rates.

Depends: Sinus bradycardia is a normal rhythm. It's a semantic question but i don't think most cardiologists would consider it an arrhythmia. Pathologic bradycardias such as due to 2nd or 3rd degree heart block would surely be considered an arrhythmia.