"Natural" heart pacemakers made from human stem cells have been successfully tested in pigs.
Tests in pigs "proved the concept"
Ultimately, this technology could replace the electronic pacemakers currently used to treat humans with irregular heartbeats, scientists hope.
The Israeli team from Technion-Israel Institute of Technology, along with US colleagues, took the stem cells from donated human embryos.
The process is described in the journal Nature Biotechnology.
In healthy hearts, groups of special heart cells make the organ beat regularly by stimulating the heart muscle cells to contract.
In people where this mechanism fails, an electronic, battery-powered pacemaker is implanted to keep the heartbeat going.
These devices may need replacing and some electrical equipment, such as certain mobile phones, can interfere with the way they work.
In comparison, "natural" pacemakers made from the body's own cells would need no power source and would become part of the heart.
Dr Lior Gepstein and his team took embryonic stem cells and used chemicals to coax them to grow into standard heart muscle cells.
Some of these cells were seen to beat spontaneously in the same way as healthy heart muscle.
The scientists isolated these cells and injected them into the hearts of pigs with abnormally slow heart rates.
In 11 out of 13 pigs, the injected cells produced their own heart rhythm.
In five of the pigs, this was limited to short bouts, but in six of the pigs the beat was sustained and resembled the pattern of a normal beating heart.
The researchers said their research provided evidence that the same technique could potentially be used to make a "biological pacemaker" to treat human patients with heart conditions.
"Our proof-of-concept study suggests the use of excitable cell grafts as a biological alternative to implantable devices," they said.
But they added: "Nevertheless, several obstacles must be overcome before this strategy can reach the clinic."
There is a theoretical risk that the cells could become cancerous or that the body would reject the cells.
But, on the positive side, the embryonic stem cells have the advantage over other cell candidates for repairing hearts of being able to be made in unlimited numbers, the scientists said.
Dr Tim Bowker, Associate Medical Director of the British Heart Foundation, said: "This study provides interesting findings about human heart cells grown from stem cells, and used in laboratory experiments on animal heart tissues.
"The BHF supports stem cell research, but the use of the techniques described is a long way from clinical application in humans.
"Use of stem cells in the treatment of heart disease has been proposed for a range of heart conditions, and this research adds to this list of potential future applications for stem cells in treating Britain's biggest killer."