The human heart beat is powered by chemical impulses produced by special cells called pacemaker cells. These cells are often affected by external stimuli– medication, stress, and physical activity, just a few things that change body chemistry; altering chemical impulses, increasing or decrease heartbeat. One of the most well-known and often misunderstood external heart stimuli is defibrillation.

Defibrillation is the administration of a jolt of electricity to the heart which depolarizes the heart muscle and allows the heart's natural pacemaker to potentially reset and continue beating. Defibrillation is performed by devices called defibrillators, which vary in design and ability. Currently, the familiar TV and movie trope of defibrillator paddles being used on flat-lining patients is outdated. More commonly, defibrillation will occur via the prophalayctic nodes, which are attached to the chest of the patient and also used to monitor heart rate. These nodes deliver shocks when a shockable heart rhythm occurs. Unlike TV shows, a shocked patient does not convulse, usually there is only a small amount of muscle contracting through the body. Also, unlike media murals, a flat line is usually an 'unshockable' rhythm. Ventricular fibrillation is a 'shockable' heart rhythm and is when the ventricles quiver rather than work in a pattern. Ventricular tachycardia, another shockable rythmn, is an extremely fast rhythm in which there is a loss of pulse. Certain types of cardiac arrhythmias may not be shockable depending on severity and rhythm type. Defibrillator devices in hospitals are usually not fully automatic, but are very similar to the completely automatic AEDs by Cardiac Science, Zoll, Phillips HeartStart, and Samaritan.

The Cardiac Science Powerheart G3 Portable AED Defibrillator is designed to be easy to use in an emergency cardiac arrest situation. The Powerheart Portable Automatic External Defibrillator features a text screen, convenient for noisy and chaotic environments, which runs in tandem with the voice prompts. The device displays the patient's heart rate, the waveform, number of shocks delivered, and the elapsed time. The Powerheart Defibrillator features built in automatic synchronization and pacemaker pulse detection.

The Zoll AED Plus is a unique unit in that it is completely automatic, but also it is the only full-rescue AED, walking the user through the full “Chain of Survival” by supporting CPR. Not only does the Zoll AED Plus track a shockable heartbeat, it also tracks chest compressions by the rescuer and advises on pace and compression strength. The Zoll AED Plus provides Real CPR help, providing visual and audio feedback and instructions. The HeartStart OnSite AED likewise provides audible commands when in use, and walks the rescuer through potential defibrillation, if a shockable rythmn is detected. The Samaritan PAD Public Access Defibrillator AED is specifically designed for public access use. All of these AEDs use verbal and visual prompts to guide the rescuer. The AEDs let the rescuer know when to touch and when not to touch the patient. If a shock is required, there will be a visual clue.