I won't claim or insist that the drug has/had no bearing on your heart's rate, but unless you have unmistakable symptoms associated with low heart rate, things such as swelling in the ankles, shortness of breath, feeling dizzy when you stand from seated, fainting....your heart rate is NOT too low....for you.................so far.

This is where you are cautious, maybe keep records of odd sensations or events, especially of the kind I listed just now, when they took place, and under what conditions, and report those to your prescribing physician after a few (more) days. It's still early, and you've had no dangerous events.......?

I am happy to see you are aware of your HR, that you are self-monitoring. Keep it up...but don't assume that an HR in the 50's is danger territory. Many healthy hearts in fit people, athletes particularly, run in the low 40's, if you can believe it. When I was in my 40's donkey's years ago, and a competitive runner, my resting HR was 38, and that was sitting on the upstairs can after running up two flights of stairs to get there....about 30 seconds rest doing my business and then taking a pulse just for giggles. Thirty-eight beats per minute. Yes, the medical literature says <60 BPM is technically bradycardia territory, but cardiologists will gently say it's just a guideline, probably meant more for the elderly who might be in danger of a fall if their BPM dips to 50 BPM.

So, once again, please give it another few days, do keep an eye and record your rates several times each day, and do get ahold of your PCP if you have any unmistakable reactions to your low(er) heart rate.