An arrhythmia is an abnormal heart rhythm. Atrial fibrillation is the most common type of irregular heart rhythm in the United States. It originates in the atria, the heart's two upper chambers, and increases the risk of a stroke. In patients with atrial fibrillation, the electrical signal that normally causes the heart’s atria to contract in an orderly fashion circles through the heart muscle in an uncoordinated manner, causing the upper chambers of the heart to quiver rapidly. Initially, medications may be used to treat atrial fibrillation, however some patients will be candidates for surgery, and your cardiologist and surgeon will discuss treatment options with you.