MedPage Today -- Patients with implantable cardioverter-defibrillators or pacemakers should avoid placing the headphones from their MP3 players too close to their chests, researchers said. That’s because the magnets in portable headphones may cause the cardiac devices to temporarily malfunction, William Maisel, MD, MPH, of Beth Israel Deaconess Medical Center in Boston, and colleagues reported in the October issue of Heart Rhythm.