Can an atrial fibrillation be lethal?

Yes: When the heart is in atrial fibrillation, it causes blood to clot in the chambers of the heart. These clots can flow out of the heart and cause strokes. Strokes can be lethal. Doctors sometimes put people on a blood thinner called warfarin (coumadin) to help prevent clots in people with atrial fib. It's a serious condition, but manageable! cheers!

Only if…: Only if the atrial rate is conducted in a very rapid fashion to the lower chamber. Your heart has built-in protection to keep this from happening. However, patients with a condition known as Wolff-Parkinson-White sometimes lack this protection and under the right circumstances can die as a result of atrial fibrillation.