Atrial fibrillation (AF ) is abnormal heart rhythm or cardiac arrhythmia that involves the two upper chambers or atria of the heart. It can often be identified by taking a pulse and observing that the heartbeats don't occur at regular intervals, but a conclusive indication of AF is the absence of P waves on an electrocardiogram (ECG).

In Atrial fibrillation, 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.

Atrial fibrillation is often asymptomatic, and is not in itself generally life-threatening, but  Atrial fibrillation is usually accompanied by symptoms related to a rapid heart rate. Rapid and irregular heart rates may be perceived as palpitations, exercise intolerance, and occasionally produce angina  and congestive symptoms of shortness of breath or edema. Sometimes the arrhythmia will be identified only with the onset of a stroke and TIA or transient ischemic attack.

A thromboembolism is said to occur when a thrombus that became an embolus plugs a blood vessel and prevents blood from flowing. The damage produced by an embolus is related to where the circulation takes it. An embolus that ends up in the brain produces the most feared complication of atrial fibrillation, namely stroke.

People with Atrial fibrillation  are often given anticoagulants such as warfarin to protect them from stroke. Surgical and catheter-based therapies may also be used to prevent recurrence of AF in certain individuals.