If you own a portable music player, you probably know the headphones are powerful enough to damage your hearing.

But you might NOT know that the magnets in those headphones pose another danger.

They could interfere with implanted cardiac devices such as pacemakers and defibrillators.

That’s the conclusion of a study published recently in the journal Heart Rhythm.

In the study, researchers tested eight models of headphones.

Six of them were earbuds, worn inside the listener’s ear canal. The other two were clip-on models that attach to the top of the outer ear.

Using an instrument that measures magnetic fields, researchers found vast differences between the headphones.

One clip-on emitted a magnetic field about thirty times as strong as the weakest earbud.

Researchers also tested the headphones with one-hundred cardiac patients.

In thirty percent of the tests, headphones interfered with the devices at a distance of two centimeters.

The effects included altered rhythm in pacemakers, and temporary shutdown in defibrillators.

Fortunately, none of the patients were harmed.

In fact, there are no documented cases of stereo headphones causing harm to anyone with an implanted cardiac device.

Nonetheless, researchers warned that it could happen.

They suggest a few precautions: If you wear an implant, never stow headphones in a shirt pocket or dangle them around your neck.

Similarly, don’t let anyone who’s wearing headphones put their head on your chest.

Maybe this all sounds a little bit paranoid.

But when it comes to heart health, you don’t want to miss a beat.

So play it safe and play your music safely.