1. A procedure for restoring normal, efficient rhythm to a heart with an irregular beat by passing an electric current through it.
2. The termination or ending of an arrhythmia (irregularity in the rhythm of the heartbeat) with a counter electric shock.
3. In extreme cases of paroxysmal tachycardia (a sudden, abnormal intensity and rapid beating of the heart), a procedure in which an electric shock is administered directly to a patient's heart while he or she is under a mild anesthetic.