Atrial fibrillation (AF) is the most common, abnormal rhythm of the heart.
The heart contracts (beats) and pumps blood with a regular rhythm, for example, at a rate of 60 beats per minute there is a beat every second. The heart may beat faster or slower with a shorter or longer interval between beats, but at any one rate the interval between beats is constant. This regular rhythm occurs as a result of regular electrical discharges (currents) that travel through the heart and cause the muscle of the heart to contract. In atrial fibrillation, the electrical discharges are irregular and rapid and, as a result, the heart beats irregularly and, usually, rapidly.
Atrial fibrillation is common; half a million new cases are diagnosed yearly in the U.S., and billions of dollars are spent annually on its diagnosis and treatment.