Atrial fibrillation is a common abnormal heart rhythm. In patients with atrial fibrillation, the upper heart chambers (atria) do not contract (fibrillation) because they are paralyzed by continuous electrical activity. However, the continuous electrical activity tries to pass to the lower heart chambers (ventricles). Fortunately, only some of this electrical activity is allowed to pass. However, the heartbeat becomes rapid and irregular, often leading to less efficient pumping of blood and symptoms. Sometimes atrial fibrillation is of unknown cause, but it is often associated with underlying heart conditions, high blood pressure, overactive thyroid, or too much alcohol. Some people with atrial fibrillation have no symptoms, while others have a fluttering sensation in the chest, lightheadedness, shortness of breath, or chest pain. A dangerous complication of atrial fibrillation is stroke. Stroke occurs because blood clots form in the paralyzed atria and can travel to the brain. Blood thinners (anticoagulation) can prevent stroke in patients with atrial fibrillation. Other treatments include medications to slow the heartbeat (rate control) or to convert it to normal rhythm (cardioversion). Doctors can use medications (medical cardioversion) or electricity (electrical cardioversion) to change atrial fibrillation to normal rhythm. Studies showed that medications to slow the heartbeat and thin the blood are the best treatment for most patients with atrial fibrillation. Because studies show that rhythm control and rate control are similarly effective, economic factors will play a role in the selection of treatment.