Cardioversion:

Cardioversion is a procedure used to return an abnormal heartbeat to its normal rhythm. It is done when the conducting system of the heart is fast or irregular, in other words when there is a condition called arrhythmia. Cardioversion is an electrical high-energy shock sent to the heart to reset its rhythm to normal. An abnormal heart rhythm might beat quickly causing your heart to not have enough time to fill with the needed amount of blood to pump to the rest of your body with every beat. In addition, some types of abnormal heart rhythms may raise your risk of strokes or sudden death. A successful cardioversion allows the heart to reset itself back into a normal rhythm.