Jumpy,
I had a low resting heart rate for many years before my valve surgery. I had also been a runner for 30+ years, so we just attributed the low rate to general good cardio health.
Then once my valve was replaced, all *$)@( broke loose. My heart rate did everything it wasn't supposed to do - extra beats, skipped beats, super fast (tachycardia), super slow (bradycardia), then it just stopped several times for 15-20 seconds at a time. Try as we might, the doc's couldn't get my heart regulated, and I ended up with a pacemaker. My electrophysiologist (pacemaker doc) believes that all the time before surgery I had bradycardia (unusually slow heart rate) but I was in such good shape I had no symptoms from it. BTW - I also had a bicuspid aortic valve that became stenotic.
I'm telling you all this to say that your heart rate may be like mine was. As long as you have few to no symptoms, they will often just watch it for a while. When you have surgery, though, the electronic pathways of your heart may become irritated or damaged, and you may have rhythm issues after surgery. Not to worry - if they can't fix them one way then the other way is a pacemaker. Either way, your valve will be fixed and you can go on with life.
P.S. I don't mean this post to sound too negative. On the contrary, at least for me all is well. I'm back to the gym 5 days a week.