In only six years, the small, plastic device that can hold your entire record collection has revolutionised the way we listen to music, changed society and turned the ailing Apple computer company into the dominant force in the download music industry.
But researchers are so concerned about thepotential effects of MP3 players on heart pacemakers that a major clinical investigation is starting this month.
The trial comes in the wake of a report this year that iPods may cause pacemaker interference in up to half of patients. A study in Michigan in the US found that when an iPod was held 5cm from a patient's chest for five to 10 seconds, it interfered with pacemakers in half the 100 patients, whose average age was 77.
Now researchers want to test the possible dangers with other types of player and different ages of patients.
There have been concerns about the possible interference of other gadgets with pacemakers, and mobile phones have been investigated.
One study showed that a phone being used at the ear was sufficiently far away to prevent a health risk, but recommended that phones not be put in shirt pockets or used near the implanted device.
The Boston researchers point out that, unlike phones, which are usually held to the ear, portable MP3 players can be held almost anywhere, including positions close to the site of the implanted device.
They cite the research showing that the players caused pacemaker interference with over-sensing - where the pacemaker misreads the heart's functioning - in 20 per cent of patients; interference in 29 per cent; and pacemaker inhibition, where the pacemaker stopped functioning properly for a time, in 1.2 per cent. In some cases, interference was detected when the players were 45cm away.
Those researchers said that while older people with pacemakers might not use MP3 players, they could well come close to them through contact with grandchildren.
In the Boston trial, four different brands of MP3 players will be tested at three distances from the implanted medical device in children and adults aged 4 to 55 with congenital heart disease. At each distance the pacemaker will be checked for changes in sensing and pacing.
