The AED is a device about the size of a small laptop computer that analyzes the heart's rhythm for any abnormalities and, if necessary, directs the rescuer to deliver an electric shock to a victim of cardiac arrest. This shock, called defibrillation, may help the heart to re-establish an effective rhythm of its own. . The electrical signal generated by the heart is picked up by the AED through two self-adhesive defibrillation pads. When a shock is initiated, the electric current is delivered to the patient through these. Correct positioning of the pads is important to ensure correct interpretation of the rhythm by the AED and subsequent effective delivery of the shock.