Definition: Atrial Fibrillation (AF) is the most common type of arrhythmia (problem with the heart rhythm. AF occurs when irregular electrical signals cause the upper chambers of the heart to contract very quickly and sporadically with no regular pattern. This causes blood to pool up in the atrium (upper chambers) and not move to the ventricles (lower chambers) as it should. AF can increase risk of heart failure or stroke.
Examples: Because atrial fibrillation can allow blood to pool and clot in the chambers of the heart, patients with A-fib are often put on anticoagulants to prevent blood clots from forming.