Damage caused by a heart attack has been healed using stem cells gathered from the patient’s own heart, according to doctors in the US.

The amount of scar tissue was halved in the small safety trial reported in the Lancet medical journal. The authors said there was also an “unprecedented” increase in new heart muscle.

The British Heart Foundation said it was “early days”, but could “be great news for heart attack patients”. A heart attack happens when the organ is starved of oxygen, such as a clot blocking the flow of blood to the heart.

As the heart heals, the dead muscle is replaced with scar tissue, but because this does not beat like heart muscle the ability to pump blood around the body is reduced.

Within a month of a heart attack, a tube was inserted into a vein in the patient’s neck and was pushed down towards the heart. A sample of heart tissue, about “half the size of a raisin”, was taken.

This was taken to the laboratory where the stem cells were isolated and grown. Up to 25 million of these stem cells were then put into the arteries surrounding the heart.

Twenty five patients took part in the trial. Before the treatment, scar tissue accounted for an average of 24% of their left ventricle, a major chamber of the heart. It went down to 16% after six months and 12% after a year.

Healthy heart muscle appeared to take its place. The study said “the cells have an unprecedented ability to reduce scar and simultaneously stimulate the re-growth of healthy [heart] tissue”.