Atrial fibrillation (AF or A-fib) is the most common cardiac arrhythmia (abnormal heart rhythm), and involves the two upper chambers 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 do not 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...