Here are two links you'll definitely want to check out. They are from About.com. The first is a short, two minute video that explains atrial fibrillation, which many Grave's Disease patients will experience. I did.
The second is a short video that describes the effects of tachycardia (rapid heart beat), another symptom you might experience as a result of Grave's Disease or Hyperthyroid.
While you are on the site you might want to sign up for the e mail's from Dr. Richard Fogoros M.D. You'll find many useful articles throughout the week.