Scientists have identified rare stem cells in the hearts of newborns, which could be used to treat babies with cardiac problems.
The treatment could help newborn babies with heart defects
The cells form heart muscle in the developing foetus.
But the University of California study, published in Nature, showed some of the cardiac progenitor cells were still present in babies' hearts after birth.
They proved the cells could form working heart tissue which could be used as a treatment.
The researchers suggest that the subset of isl1+ cells are left over after the development of the foetal heart to oversee the formation of a mature heart in newborn babies, who are no longer relying on their mother's circulation and oxygen supply.
The cells are located in a region of the heart called the atrium.
They are also present in the hearts of newborn rats and mice.
Grown in the lab'
The researchers used genetic tags to mark the progenitor cells in living embryonic tissue and in the newborn heart of mice.
This allowed them to see that the isl1+ progenitor cells were spontaneously able to form cardiac muscle tissue.
The muscle cells which formed performed all the functions that would be seen in normal heart tissue - they were able to contract and pump.
They also worked with existing cardiac muscle cells in producing normal electrical heart beats.
They are programmed to become spontaneously beating cardiac muscle cells simply by being exposed to other neighbouring heart cells, the researchers said.
It was found millions of progenitor cells could be grown in the lab using a supportive network of tissue cells called fibroblasts.
Kenneth Chien, director of the UCSD Institute of Molecular Medicine, who led the research, said: "Conceptually, these cells could provide a cell-therapy based approach to paediatric cardiac disease, which is new for cardiology.
"Traditionally, paediatric cardiologists and cardiac surgeons have relied on mechanical devices, human and synthetic tissue grafts, and artificial and animal derived valves to surgically repair heart defects.
"While progenitor cells won't grow a whole new heart, our research has shown that they can spontaneously become cells from specific parts of the heart by simple co-exposure to other heart cells, which could augment existing surgical procedures.
"If the cells maintain pacemaker function when placed in the intact heart, they might serve as biological pacemakers for infants born with heart block, which could also be valuable."
Dr Karl-Ludwig Laugwitz, who also worked on the study, added: "The isl1+ cells potentially could be harvested from an individual's heart tissue, multiplied in a laboratory setting, then re-implanted into the patient."
Professor Jeremy Pearson, Associate Medical Director of the British Heart Foundation, said: "This paper provides the first clear description of stem cells, present in the heart and capable of proliferating and differentiating into fully competent contractile cells.
"Although there has been some evidence of the existence of this kind of cell in the heart, previous work has been disputed and probably did not even detect the cells now found by the University of California team."
He added: "Their research is truly ground breaking, with likely significant dividends not only for a better understanding of how the human heart develops but also for designing ways to manipulate this stem cell population to repair either congenital heart defects or adult hearts damaged by a heart attack."