What Is Atrial Fibrillation (AFib)?

Atrial fibrillation — universally abbreviated as AFib or AF — is the most common sustained cardiac arrhythmia (abnormal heart rhythm) in the world. It affects approximately 2.7–6.1 million Americans, with the number expected to double or triple by 2050 as the population ages. AFib is not immediately life-threatening in most cases, but it carries serious consequences — most critically, a 4–5 times increased risk of stroke — and significantly affects quality of life. Understanding what AFib is, how it causes problems, and how it is treated helps patients manage this condition effectively.

The Normal Heart Rhythm

Normally, each heartbeat begins with an electrical impulse generated by the sinoatrial (SA) node — a small cluster of specialized cells in the right atrium. This impulse spreads in an orderly wave across both atria, causing them to contract and push blood into the ventricles. The impulse then passes through the atrioventricular (AV) node — which acts as a gatekeeper and timing delay — and travels down the His-Purkinje system to activate both ventricles simultaneously, producing a coordinated, efficient ventricular contraction.

In a healthy person at rest, this cycle repeats 60–100 times per minute in a perfectly regular rhythm — the normal sinus rhythm.