Change In Pulse, Rhythm Disorder, Heart Valve Surgery
Thanks for posting your query.
The changes in your pulse rate that you describe, could be the sign of a rhythm disorder. If you do not get an symptoms along with the changes, such as palpitations, dizziness, fainting or weakness, there may not be a cause for worry.
I would recommend that you get some tests done to rule our rhythm disorder. The heart beats synchronously because of electrical wiring of heart. There are nodes present in the heart which control the rhythm. Rhythm disorders occur when there is some problem in the electrical wiring or the nodes. A heart valve surgery such as the one you had, can damage the wiring.
Some tests that you will need are an electrocardiogram and electrophysiological studies (EP) that are done by some Cardiologists. IF EP study is normal, you may need to get a Tread Mill Test done.
Avoid using the treadmill till you get tested.
Hope I have answered your queries. I am also available for your follow ups.