Atrial fibrillation (AF or afib) is a cariac arrhythmia (abnormal heart rhythm) that involves the two upper chambers (atria) of the heart. It can often be identified by taking a pulse and observing that the heart beats don't occur at regular intervals, but a conclusive indication of AF is the absence of P waves on an electrocardiogram (ECG). AF is the most common arrhythmia; 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. This may be continuous (persistent or permanent AF) or alternating between periods of a normal heart rhythm (paroxysmal AF). The natural tendency of AF is to become a chronic condition. Chronic AF leads to a small increase in the risk of death.