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The Debunker: Can Defibrillators "Restart" a Stopped Heart?

by Ken Jennings

In July 1820, Danish scientist Hans Christian Oersted published a groundbreaking pamphlet on the relationship between electric current and magnetic fields, effectively kicking off our modern electric age. You may think about electromagnetism every July when you look at your power bill and see how it spikes when your air conditioner is on. In honor of everyone getting zapped by the electric company this month, we've asked Jeopardy!'s Ken Jennings to set us straight on some high-voltage misconceptions about electricity, correcting all of our shocking ignorance. He knows "watts" up. He keeps current.

The Debunker: Can Defibrillators "Restart" a Stopped Heart?

If TV medical dramas have taught me nothing else, it's this: you can magically turn a dead person into a not-dead person by rubbing two little paddle things together, yelling "Clear!" and jolting them in the chest. L.A. improv classes probably spend at least two or three sessions practicing the "defibrillator jerk" they'll need to master if they're ever going to play Heart Attack Patient #2 on Code Black.


But Hollywood may have given you the wrong idea about what defibrillator machines actually do. In simplest terms, defibrillators cannot start a stopped heart. In fact, they work by stopping a heartbeat—a weird, problem heartbeat, that is. A powerful electric shock can actually CTRL-ALT-DELETE a heart that's pumping irregularly or too fast, in hopes of resetting the heart to its correct rhythm.

So if defibrillators don't really start a heartbeat, why are medical personnel always shocking flat-lined patients in TV and movies? That's an excellent question. In reality, once your electrocardiogram has flatlined, defibrillation isn't an option. Doctors would have to get the electrodes onto you earlier—four minutes or less following cardiac arrest, while there's still some electrical activity in the heart.

Hollywood defibrillations also tend to lag behind the times technologically. For example, on new defibrillator models, the electrode paddles are only rubbed together to spread some conductive gel, not to build up a charge. In fact, the new machines don't even need that iconic charge-up whine that builds audience anticipation—though many add it as an artificial sound effect, so as not to confuse doctors and EMTs.

Bottom line: in an actual heart attack situation, don't leap in with a short-circuited electrical wire just because you think that's what MacGyver would do. I hope that's all perfectly…"Clear!!!"

Quick Quiz: What kind of device does the Tin Man receive from The Wizard of Oz in lieu of a heart?

Ken Jennings is the author of eleven books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at or on Twitter as @KenJennings.

(Editor's note: this article was updated at Ken's request to correct an error.)