Defibrillation is a method of emergency medicine that can stop ventricular fibrillation or pulseless ventricular tachycardia. An electricity is used to reset the electrical state of the heart so that heart beat will have rhythm controlled by its pacemaker. This is not used in asystole and pulseless electrical activity. Defibrillator is used to give an electric shock to the heart. This depolarizes the muscles in the heart which stops the dysrhythmia, the SA node can eventually produce its own electrical impulse which establish the normal sinus rhythm of the heart. Cardioversion can also be done to provide normal rhythm in poorly perfusing cardiac dysrthymias.
Defibrillators can be implanted, external, transvenous depending on the type of devide used or needed in the current situation.