Atrial fibrillation (AF) is the most common abnormal heart rhythm. It is a very fast, uncontrolled heart rhythm that occurs when the upper chambers (the atria) of the heart try to beat so fast that they only can quiver. Treatment options, such as electrical cardioversion, deliver shocks to the heart, jolting it out of atrial fibrillation. Another treatment option, ablation, involves cauterizing the hearts tissue so that it can not sustain the AFIB.