Atrial fibrillation is the most common type of persistent, irregular heartbeat (cardiac arrhythmia). In atrial fibrillation, the heart's upper chambers beat irregularly, affecting blood flow to the heart muscle and to the rest of the body.

Atrial fibrillation increases the risk of blood clots, which can cause a transient ischemic attack (TIA), stroke, or other problems.

The heartbeat may return to normal on its own, or it may require medicine or electrical shock (cardioversion). Medicines called anticoagulants (blood thinners) are usually needed to prevent stroke and other complications if the heart cannot be returned to its normal rhythm.