Okay, after reading what felt like a dozen fics where ninjas/Wizards/SOLDIERS used something akin to a defibrillator:

These devices DO NOT revive you!!! They kill you. Quite effectively at that.

You use a defi, if the heart is beating so fast, that it cannot contract and pump blood anymore. The shock makes it stop.

After that you pray for it to start working normally again ON ITS OWN. (or help with a heart massage) How can anyone think that sending a few thousand volts through one’s body would HELP the heart?

Uhm, yeah. Frustrated rant over now.

Oh, and if you are lucky and the patient survives, than he will NOT be wake up for at least a few hours. Even if you did everything right. Dying is quite exhausting, after all.