What Is Atrial Fibrillation?
Atrial fibrillation, often referred to as "afib", is an irregular heartbeat, a rapid heartbeat, or a quivering of the upper chambers of the heart, called the atria. Atrial fibrillation is due to a malfunction in the heart's electrical system, and is the most common heart irregularity, or cardiac arrhythmia. For more detail about how the heart works and what happens to the heart when it is in atrial fibrillation, see About the Heart.
Source: 2019 National Health Observances, National Health Information Center, Office of Disease Prevention and Health Promotion, U.S. Department of Health and Human Services, Washington, DC.