Atrial fibrillation is one of the most common types of irregular heartbeat (cardiac arrhythmia). In atrial fibrillation, the heart's upper chambers beat irregularly.

Atrial fibrillation increases the risk of blood clots. Blood clots 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, electrical shock (cardioversion), or other procedures to stop the arrhythmia. Medicines called anticoagulants (blood thinners) are usually needed to prevent stroke and other complications if the heart cannot be returned to its normal rhythm.