Stem cells, the body's master cells, are an effective treatment for patients who have had a heart attack, researchers have found.
Stem cells are taken from the patient's own bone marrow
Sixty patients were treated either with stem cells taken from their own bone marrow, or with the best conventional treatment.
After six months, it was found the hearts of those who received the stem cell transplants were working better.
The University of Freiberg research is published in The Lancet.
Stem cells have the capability of turning into any other cell. In this case, scientists believe they turn into new blood vessel or heart muscle cells.
Patients who undergo the procedure have stem cells taken from their own bone marrow and injected directly into the heart muscle.
Because the stem cells come from the patient's own body, the transplant will not be rejected.
In this study, the researchers found that the treatment had improved the functioning of the heart's left ventricle by 7%.
In comparison, the patients given the best medical therapy but no transplant saw a 0.7% improvement in their condition.
The scientists said the beneficial effects could not be explained solely by bone marrow cells transforming into heart muscle.
Instead they believe the stem cells promoted the secretion of chemicals by heart tissue that encouraged growth.
Dr Helmut Drexler, from Germany's University of Freiburg, who led the research, said the team's findings supported the idea that a patient's own bone marrow cells could be used to help them recover after a heart attack.
But he added: "Larger trials are needed to address the effect of bone marrow cell transfer on clinical endpoints, such as the incidence of heart failure and survival."
Ian Rosenberg, a UK heart attack patient who had the pioneering treatment in Germany, was so impressed at how it changed his life that he set up a charity to fund stem cell research in the UK.
He told BBC News Online: "It was a miracle. For over two years, I couldn't get around and go out. I had to have my bedroom downstairs.
"Now I can run up and down all the time. It didn't happen immediately, but I gradually felt better over around six to eight weeks."