Once the fibrillation stops -- that is, the heart stops altogether -- the person is dead and no amount of resuscitation will bring them back.

I was trained to use a defibrillator in an applied first aid course I did a month ago. They are designed to do as their name says -- defibrillate, and get the heart beating properly again.

More and more defibrillators are being located in places such as shopping centres and business centres so a qualified first-aider can act quickly and within the timeframe that Shimagnolo mentions.