Transplanting genetically engineered cells into the heart may reduce the risk of a fatal condition which occurs after heart attack, research suggests.
Ventricular tachycardia can be fatal
Ventricular tachycardia - an unusually fast heart rhythm - is the main cause of sudden death after heart attack.
In mice, transplants of skeletal muscle cells engineered to produce a specific protein prevented the condition.
Experts said the study in Nature should help to direct research on using stem cells to treat heart attacks in humans.
The German researchers tested a variety of cells in mice who had been induced to have heart attacks.
They found that heart cells taken from 15-day-old embryos reduced the risk of ventricular tachycardia but other implanted cells, such as skeletal muscle cells, did not.
It was found that a protein present in embryonic heart cells but not the other cells - connexin 43 - was the key.
By engineering skeletal muscle cells, which are more readily available than embryonic cells, to produce connexin 43, the researchers found the cells were equally effective in preventing heart arrhythmia.
Tests on the ability of the implanted cells to conduct an electrical current - an important function of heart cells - found the signal was passed between implanted and existing heart tissue.
Study leader Dr Bernd Fleischmann, from the University of Bonn, said more research would have to be done before the technique could be used in humans but the study was important.
"The incidence of ventricular tachycardia dropped by 60%.
"We clearly showed these cells improved electrical stability.
"The nice thing about skeletal muscle is it has adult stem cells so you can take a biopsy of the thigh muscle and grow millions and millions of cells in culture."
He said there were ongoing clinical trials using skeletal muscle and bone marrow cells to try and restore pump function of the heart but this was the first study to look at arrhythmias.
Current treatment for patients who develop ventricular tachycardia after a heart attack is for a defibrillator to be implanted under the skin.
The expensive device gives a painful electric shock if it detects a fast heart beat.
Dr Tim Chico, an expert in vascular development at the University of Sheffield, said the study was preliminary.
But he added: "If it can be repeated in humans it would be a breakthrough in the treatment of patients with heart disease and could save thousands of lives."
British Heart Foundation medical director, Peter Weissberg, said: "This is a vital insight, only possible from animal studies, which should help direct current research using stem cells to prevent the dangerous consequences of heart attacks in people.
"However, application of this technique to people with heart disease is still a long way off."