The scars caused by a heart attack have been healed by stem cells collected from the patient's own heart, U.S. experts have said.

The research, which was reported in the Lancet medical journal, found that the amount of scar tissues was halved in the small safety trial.

Heart attack occurs when the heart falls short of the right amount of oxygen due to a clot blocking the flow of blood to the heart.

The trial

This trial, which was conducted at the Cedars-Sinai Board of Governors Heart Stem Cell Center, involved 25 patients.

A tube was inserted into a vein in the patient's neck and was pushed down towards the heart to collect a sample of heart tissue. This process of collecting the sample was done on the patient within a month of the heart attack.

This sample was taken to the laboratory where the stem cells were isolated and grown.

During the treatment, up to 25 million of these stem cells were put into the arteries surrounding the heart. Before the treatment, scar tissues accounted for an average of 24 percent of their left ventricle, a major chamber of the heart. After the treatment it went down to 16 percent after six months and 12 percent after a year.

Dr Eduardo Marban, one of the researchers, was quoted by the BBC as saying: While the primary goal of our study was to verify safety, we also looked for evidence that the treatment might dissolve scar and regrow lost heart muscle.

This has never been accomplished before, despite a decade of cell therapy trials for patients with heart attacks. Now we have done it. The effects are substantial, and surprisingly larger in humans than they were in animal tests, he added.

However, Prof Anthony Mathur, who is co-ordinating a stem cell trial involving 3,000 heart attack patients, argued that as it was a proof-of-concept study, with a small group of patients. He said: The findings would be very interesting, but obviously they need further clarification and evidence.

Prof Jeremy Pearson, associate medical director at the British Heart Foundation, said that this is the first time any such finding has been carried out in humans. The results are very encouraging, he added.

These cells have been proven to form heart muscle in a petri dish but now they seem to be doing the same thing when injected back into the heart as part of an apparently safe procedure, Pearson said.

It's early days, and this research will certainly need following up, but it could be great news for heart attack patients who face the debilitating symptoms of heart failure, Pearson added.