Atrial fibrillation is an irregular heart rhythm affecting about 3 million Americans. The most serious risk of atrial fibrillation is stroke, caused by a blood clot forming in the abnormally beating heart chambers and traveling to a blood vessel in the brain. For over 50 years the mainstay of atrial fibrillation treatment has been the anticoagulant warfarin (better known by the brand name Coumadin) which effectively decreases the risk of stroke by preventing blood clots. By the way, medicines t...