Stem cells have been used to save mice embryos from a lethal heart defect.
Science has high hopes for stem cell therapy
Scientists from New York injected embryonic stem cells into mouse embryos bred to develop a heart problem.
Not only did the cells develop into healthy heart tissue, they also sent out messages correcting defects in neighbouring cells.
Giving a mother a shot of stem cells before she became pregnant was also enough to save future embryos, the research reported in Science found.
The scientists, from Memorial Sloan-Kettering Cancer Center and Weill Medical College, hope their work will eventually lead to new treatments for adult cardiac diseases.
They say that stem cells are able to influence neighbouring cells by secreting two key signalling molecules.
One, WNT5a, works over a short distance, while the second, IGF1, seems to exert its influence over a longer distance.
Researcher Dr Robert Benezra said: "Stem cells act like nurses, restoring 'sick' cells to health."
The researchers had previously identified a protein called Id as playing a key role in the development of an embryo's blood vessels.
The mice in the latest study were engineered to lack this protein. As a result, without stem cell treatment they were likely to develop severe cardiac defects, and die before birth.
The New York team also found that stem cells deprived of Id themselves had far less positive impact on defective heart tissue.
Dr Anthony Mathur, a cardiologist at Barts and the London NHS Trust who is carrying out research using stem cells, told BBC News Online that any work which provided more clues about how to repair heart defects was potentially important.
However, he said the use of embryonic stem cells was highly ethically controversial.
There were also issues about the safety of introducing foreign material into the heart.
"Other work has suggested embryonic stem cells are probably going to be the best type to use to try to repair damaged organs," he said.
"But their use presents massive issues which need to be overcome."
Stem cells can be taken from other sources, such as adult tissue, but scientist believe those taken from embryos probably have the greatest potential for medical use.