An automated external defibrillator is used to detect and treat emergency severe heart arrythmia such as ventricular fibrillation (v-fib) and ventricular tachycardia (v-tach). V-fib is a condition wherein the cardiac electrical system is erratically pulsating, resulting in an ineffective transfer of blood from the heart to the body (and brain), which ends in cardiac arrest. V-tach is a condition wherein the heart is beating too fast to render effective transfer of blood from the heart to the body (and brain). A defibrillator clears the electrical system (a reboot of sorts) and allows it to start over.

The Automated External Defibrillator is automated in that the shock level is not user-selectable, and the user cannot override "no shock" advice. It is external in that there are pads that are attached to the patient/victim, rather than an implant surgically placed in the patient/victim's chest.

All AEDs manufactured and approved for use in the US feature a synthesized voice prompting the user or users through every step of use.\n