Did they start you on beta blockers after surgery?
It is not normal and there can be a number of reasons such as damage to heart tissues, high blood pressure, complication from heart surgery, underactive thyroid gland, medication, electrolyte imbalance, etc.
The risk is when the heart rate is slow there exits a possibility there is not enough blood pumped into circulation, etc. If too low you can have a fainting spell as well. You probably should get a doctor's evaluation of your bradycardia.
Thanks for your question, and if you have any follow up questions or comments you are welcome to respond. Take care,
Ken