To expand a bit more. An AED, (automatic external defibrillator) will only shock if it detects a shockable heart rhythm, and there are only 2 rhythms that are shockable. If the patient has flat-lined an AED isn't gonna help other than to let you know it won't shock them. The only 2 shockable heart rhythms are Vtach and Vfib. No matter what you see on television, you can't restart a heart that's in asystole with an AED.

If there's no detectable electrical activity in the heart, the AED won't help.

Anyone care to guess where they were first publicly installed and used regularly?