The researchers, based in Haifa, Israel, said there were still many years of testing and refining ahead. But the results meant they might eventually be able to reprogram patients' cells to repair their own damaged hearts.

"We have shown that it's possible to take skin cells from an elderly patient with advanced heart failure and end up with his own beating cells in a laboratory dish that are healthy and young - the equivalent to the stage of his heart cells when he was just born," said Lior Gepstein from the Technion-Israel Institute of Technology, who led the work.

The researchers, whose study was published in the European Heart Journal on Wednesday, said clinical trials of the technique could begin within 10 years.

Heart failure is a debilitating condition in which the heart is unable to pump enough blood around the body. It has become more prevalent in recent decades as advances medical science mean many more people survive heart attacks.

At the moment, people with severe heart failure have to rely on mechanical devices or hope for a transplant.

Researchers have been studying stem cells from various sources for more than a decade, hoping to capitalize on their ability to transform into a wide variety of other kinds of cell to treat a range of health conditions.

There are two main forms of stem cells - embryonic stem cells, which are harvested from embryos, and reprogrammed "human induced pluripotent stem cells" (hiPSCs), often originally from skin or blood.

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Gepstein's team took skin cells from two men with heart failure - aged 51 and 61 - and transformed them by adding three genes and then a small molecule called valproic acid to the cell nucleus.

They found that the resulting hiPSCs were able to differentiate to become heart muscle cells, or cardiomyocytes, just as effectively as hiPSCs that had been developed from healthy, young volunteers who acted as controls for the study.

The team was then able to make the cardiomyocytes develop into heart muscle tissue, which they grew in a laboratory dish together with existing cardiac tissue.

Within 24 to 48 hours the two types of tissue were beating together, they said.

In a final step of the study, the new tissue was transplanted into healthy rat hearts and the researchers found it began to establish connections with cells in the host tissue.

"We hope that hiPSCs derived cardiomyocytes will not be rejected following transplantation into the same patients from which they were derived," Gepstein said. "Whether this will be the case or not is the focus of active investigation."

Experts in stem cell and cardiac medicine who were not involved in Gepstein's work praised it but also said there was a lot to do before it had a chance of becoming an effective treatment.

"This is an interesting paper, but very early and it's really important for patients that the promise of such a technique is not over-sold," said John Martin a professor of cardiovascular medicine at University College London.

"The chances of translation are slim and if it does work it would take around 15 years to come to clinic."

Nicholas Mills, a consultant cardiologist at Edinburgh University said the technology needs to be refined before it could be used for patients with heart failure, but added: "These findings are encouraging and take us a step closer to ... identifying an effective means of repairing the heart."

(Editing by Andrew Heavens)

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