I have a root canal over a month ago and two hours after the procedure I started experiencing sudden attacks of tachycardia. Over the next week it had become extremely frequent, spending most of the day with a heart rate above 115. I was prescribed 25mg metoprolol twice a day and I still feel a pounding heart and shortness of breath randomly but it has helped keep my heart rate under 100bpm. My blood tests were normal, ekg was normal, holter monitor showed sinus tachycardia . Im still waiting to take a stress test and the results of my echo. What else could cause this? Im 32 years old, 180lbs and not in terrific shape but I am fairly active.