• When the heart stops beating properly, a defibrillator can shock it into rhythm.heart beat medical image by Nicemonkey from Fotolia.com
  
  Defibrillators are used when a person is in cardiac arrest. The machine sends an electrical impulse to the heart to jump-start it into beating again. Manufacturers have created different types of defibrillators over time; each applies to a different situation.
  
  

Manual External

• A manual external defibrillator is used in an emergency situation. The heart has usually stopped beating and needs a shock to beat again. The Manual External Defibrillator, or MED, has a monitor to keep track of the heartbeat, and paddles to administer the shock. The physician or paramedic chooses at what voltage to administer the shock and may increase the voltage if previous attempts have not restarted the heart.
  
  

Automated External

• An automated external defibrillator, or AED, is the newest on the market. A computer inside the monitor tracks the heartbeats. When it recognizes that the heart is not beating as it should, it sends a shock in an attempt to regulate the heart. During a cardiac emergency, the AED will continue to shock the heart at different levels and intervals to get it back to normal. If it does not find a heartbeat, it will continue to shock the heart to help it move blood to the brain and rest of the body. Without proper bloodflow to the brain, the chances of the person surviving or making a full recovery drastically decrease.
  
  

Implantable Defibrillator

• An implantable defibrillator is placed into the chest cavity and attached with wires to the heart. It runs on a battery. The defibrillator monitors and sends signals to the heart to help it beat at an even pace. It can be used as a pacemaker, but also has the capability to send small electrical shocks when it finds that the heart is off-beat, or beating too fast or too slow. Implantable defibrillators can also be monitored externally at a medical facility. If a major cardiac episode develops, the facility is alerted and someone can attempt to contact the patient or emergency vehicles to administer assistance. When a patient has an implanted defibrillator, he will need frequent doctor's appointments to document and discuss activity detected by the machine.