除細動器 AED
A [b]Defibrillator[/b] is medical device that sends an electric pulse or shock to the heart. 

Despite what you might see in movies and TV, defibrillators do not send an electric shock to restart your heart if it stops beating but the opposite, as the device stops your heart to help normalize your regular heartbeat if it's beating irregularly or too fast.
defibrillator