A gene inserted into ordinary heart cells transformed them into rare "pacemaker" cells that regulate cardiac rhythm, according to experiments carried out on lab rodents.

The research is a step toward the goal of a biological fix for irregular heartbeat, which at present is tackled by drugs or electronic pacemakers, its investigators said.

The heart has 10 billion cells but fewer than 10,000 of them are pacemaker cells, which generate electrical activity that spreads to other cardiac cells, making the organ contract rhythmically and pump blood.The work, reported in the journal Nature Biotechology on Sunday, uses a virus to deliver a human gene called Tbx18, whose normal role is to coax immature cells into becoming pacemaker cells.

Ordinary cells "infected" by the harmless Trojan horse were reprogrammed by Tbx 18 and became these important specialised cells."The new cells generated electrical impulses spontaneously and were indistinguishable from native pacemaker cells," said Hee Cheol Cho at the Cedars-Sinai Heart Institute in Los Angeles, California.

The promising technique builds on decade-long research into biological pacemakers. So it has so far been tested on guinea pigs and rats."We expect this to work in humans. It would be two to three years from now until the first clinical trial, the first target patients being the ones with (pacemaker) device infection," Cho said.