Any drug has risks. You are doing the right thing to have your INR closely monitored. The main risk from Coumadin is bleeding. The risks of taking Coumadin must be weighed against the risks of not treating the atrial fibrillation with it. In general studies, the risks of Coumadin causing bleeding are less than the risks of a stroke caused by the atrial fibrillation, so it is usually recommended. However, this also depends on the type of atrial fibrillation you have and what other kinds of problems you have with your heart, if any. Sometimes other drugs like aspirin or Plavix are used to thin the blood in atrial fibrillation. This is something you should discuss with your cardiologist. I presume s/he has evaluated these things and decided that Coumadin is the safest treatment in your case, but you can further clarify this with him or her to feel more comfortable with that decision. Hope this helps.