what is a. fib
Home | 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.