Research presented at an American Heart Association meeting in New Orleans found the magnets in headphones, not the actual music players, could interact with implanted cardiac devices.

Dr. William H. Maisel, senior author of the study and director of the Medical Device Safety Institute at Beth Israel Medical Center in Boston, said researchers tested eight different models of MP3 player headphones with iPods on 60 defibrillator and pacemaker patients, the AHA said Sunday in a release.

"We placed the headphones on the patients' chests, directly over where their devices are located, monitoring them for evidence of an interaction," Maisel said .

Detectable interference was observed in 15 percent of the pacemaker patients and 30 percent of the defibrillator patients.

He said patients should be instructed to keep their headphones at least 3 centimeters from their implantable devices and not place headphones in their pocket or drape them over their chest.