You stick the device's electrode pads to the patient's bare chest. ZOLL pads are designed to fit the natural shape of the body, and some models use a single, easy-to-place piece.Heart Analysis: The AED will tell you to stop CPR for a few seconds while it automatically scans the patient’s heart rhythm to see if a shock is needed.Deliver the Shock: If the device detects a shockable rhythm (like ventricular fibrillation), it will charge and instruct you to push the flashing shock button (or it will deliver the shock automatically, depending on the model and settings).