Scientists have released research denying claims that portable music players, such as iPods, can interfere with pacemakers and give some patients a heart attack.

Howard Bassen, a researcher at the US Food and Drug Administration, published his findings last week in the journal BioMedical Engineering OnLine.

The recent malfunctioning of a cardiac pacemaker, apparently caused by electromagnetic interference from a portable music player, was highly publicised around the world.

Researchers concluded that labels may be necessary to warn users against close contact between pacemakers and music players.

However, Bassen stated in his own research that an "in-vitro study to evaluate these claims found no effects".

Bassen's team measured the low-frequency magnetic field emissions from various iPod music players, each placed in 2.7cm above the pacemaker case.

"Based on the observations of our in-vitro study we conclude that no interference effects can occur in pacemakers exposed to the iPod devices we tested," he said.