Atrial fibrillation, or AF or AFib, is the most common type of arrhythmia. With AFib, your heart quivers, beats too quickly, or skips beats. It can't pump blood through its chambers and out to your body as well as it should. Sometimes blood can pool in the heart and form clots, which could lead to a stroke.

During atrial fibrillation, the heart's two upper chambers (the atria) beat erratically and irregularly — out of coordination with the two lower chambers (the ventricles) of the heart.