Atrial fibrillation (say "AY-tree-uhl fih-bruh-LAY-shun") is a type of irregular heartbeat (arrhythmia) in which the heart's upper chambers quiver, or fibrillate. This increases the risk of blood clots, which can cause a stroke or other problems. The lower chambers beat without a regular rhythm and may beat too fast. This can cause symptoms like lightheadedness or chest pain.

Treatment is done to control your heart rate or heart rhythm and to prevent stroke.