Your description is not clear enough to conclude - looks like you are having missed beats? Sometimes they occur in normal persons too.
You have not mentioned the name of your medicine - may be it contains diuretic
( cause salt losing) / Low level of electrolytes like example -potassium - may be the reason.
There are medicines for blood pressure which also have effects on heart beating - example - Beta Blockers
If it is very troublesome, they may do Holter - 24 hour ambulatory monitoring - of your beats - to get a proper idea
You ought to see your doctor / have an ECG done / and then modify your treatment
A vet should not be afraid so easily! Relax - this appears to be simple...