Sticky pads with sensors (called electrodes) are attached to the chest of the person who is having sudden cardiac arrest (SCA) and being resuscitated using CPR. The electrodes send information about the person’s heart rhythm to a processor in the AED. The processor analyzes the heart rhythm to find out whether an electric shock is needed or not. If an electric shock is needed, an AED is able to charge itself with a push of a button and also deliver a shock to the victim, trying to return the heart to a normal rhythm.