Atrial Fibrillation

Atrial fibrillation (AF or A Fib) is the most common abnormal heart rhythm. It is a very fast, uncontrolled heart rhythm that occurs when the upper chambers of the heart (the atria) try to beat so fast that they only can quiver. During AF, the upper chambers beat between 350 and 600 times per minute. Normal heart rhythm is between 60 and 100 beats per minute. Due to the erratic rhythm in the upper chambers, the rhythm of the lower chambers of the heart (the ventricles) can also become very irregular.

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Because the heart’s pumping function isn’t working properly, the blood is not completely emptied from the heart’s chambers, causing it to pool and sometimes clot. Sometimes, clotted blood dislodges from the atria and results in a stroke. The American Heart Association estimates that of the 700,000 strokes occurring each year in the U.S., 15 percent—about 105,000—occur in people with AF.

Normal Rhythm

Every normal heart has a normal rhythm. That rhythm varies from person to person. In most healthy people, the heart at rest beats about 60 to 100 times per minute. A small bunch of heart cells called the sinoatrial node keeps time.