Atrial fibrillation (AF or A-fib) is the most common cardiac arrhythmia (abnormal heart rhythm)^[1] and involves the two upper chambers (atria) of the heart. Its name comes from the fibrillating (i.e., quivering) of the heart muscles of the atria, instead of a coordinated contraction. It can often be identified by taking a pulse and observing that the heartbeats don't occur at regular intervals. However, a stronger indicator of AF is the absence of P waves on an electrocardiogram(ECG or EKG), which are normally present when there is a coordinated atrial contraction at the beginning of each heart beat.^[ Risk increases with age, with 8% of people over 80 having AF.

In AF, the normal electrical impulses that are generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles that generate the heartbeat. The result is an irregular heartbeat, which may occur in episodes lasting from minutes to weeks, or it could occur all the time for years. The natural tendency of AF is to become a chronic condition. Chronic AF leads to a small increase in the risk of death.