@gloaming knows his stuff. However, I would think the first approach would be to avoid the exercise that triggers the tachycardia, and find exercise that doesn't trigger it, whether tai chi, walking, swimming....As @gloaming implies, each time you do the elliptical @sa joe , you may be increasing the chance for longer term problems. I am only another patient so discuss with your doctor of course. (I take magnesium, potassium and CoQ10 for heart, something else to ask the doctor about perhaps...)