Four out of a group of five seriously sick Brazilian heart-failure patients no longer needed a heart transplant after being treated with their own stem cells, the doctor in charge of the research said on Monday.

Such "regenerative medicine", in which stem cells extracted from patients' own bone marrow are used to rebuild tissue, may one day become commonplace for patients with damaged or diseased hearts, some doctors believe.

Hans Fernando Rocha Dohmann of the Pro-Cardiaco Hospital in Rio de Janeiro said his four patients had such a marked improvement in blood supply after stem cell treatment that they were removed from the list of those needing a heart transplant.

"This finding has a significant social relevance since there isn't a single heart transplant programme anywhere in the world which is able to treat all the patients who need it," he told reporters at the annual meeting of the European Society of Cardiology.

The whole area of stem cell research is highly controversial because the most promising of such cells are taken from embryos, usually obtained from fertility clinics. Embryonic stem cells are capable of turning into nearly 200 different tissue types.

Still, doctors believe the field has huge potential.

"This is the first approach where you have an opportunity to actually heal a heart," said Dr Michael Rosen of Columbia University, New York. "It's going to be a very long road, but it is the most exciting thing I've seen in my 40 years as a doctor in this field."

The four critically ill patients were among a larger group of 14 who Dohmann and colleagues from the Texas Health Science Center in Houston had in April reported showing improved heart function.

Their treatment involved taking cells from bone marrow and injecting them into the heart's left ventricle, the main pumping chamber. Heart failure is the inability of damaged heart muscle to pump enough blood around the body.

Dohmann's patients belong to a small but growing number of patients being tested with the experimental therapy in centres around the world.

The exact mechanism of action is not understood but medics believe stem cells harvested from bone marrow or blood may be able to form new muscle and blood vessels. Alternatively, they may trigger a chemical reaction that improves the functioning of cells in the locality of the injection.

(Agencies via Xinhua)