This topic has been widely reported in the press since late last year when Dr. William Maisel of Beth Israel Medical Center in Boston revealed the findings of his study. Even CNN covered it.
But I just came across this video and thought it would be good to post it here.
Dr. Maisel and his team of researchers found a detectable interference with the device by the headphones in 14 of the 60 patients studied (23%). They observed that 15 percent of the pacemaker patients and 30 percent of the defibrillator patients had a magnet response.
For pacemakers, this means that the device inappropriately paced the heart without regard to the patient's underlying heart rhythm. For implantable defibrillators, this means that the ICD's antitacnycardia therapy was temporarily suspended due to the presence of the magnet.