Scientists have discovered very rare cells in newborn hearts that divide and develop into mature heart muscle and could provide a new approach to treating young cardiac patients.

The cells, known as isl1+ cardiac progenitors, were found by a team of researchers at the University of California, San Diego (UCSD), in the hearts of newborn rats, mice and humans.

“This represents the fundamental discovery of a new human heart cell, one that is programmed to become cardiac muscle but is not yet triggered to do so,” said Dr. Kenneth Chien, director of the UCSD Institute of Molecular Medicine who headed the research team.

The progenitor cells identified by Chien and his colleagues were found in areas of the heart where the bulk of congenital heart problems occur, which suggests the cells play an important role in remodelling and repairing the newborn heart.

“These cells represent an important finding because they identify clearly, using genetic tools, the cells that normally are responsible for forming the heart in the living embryo and show that a rare subset persists after birth, which is surprising,” Chien told Reuters.

Although the cells, described in the latest issue of the science journal Nature, will not become a completely new heart, Chien said they can be grown on nearby heart cells and could be used to replace mechanical devices and valves to keep young damaged hearts pumping.

“Conceptually, these cells could provide a cell therapy-based approach to cardiac disease, which is new for cardiology,” Chien said.

The scientists initially found the progenitor cells in an area of the heart called the atrium in newborn rats. They were able to genetically tag the cells in human embryonic tissue and in the hearts of mice. The cells spontaneously formed cardiac muscle tissue.

Because the cells were found in a region of the atrium that is usually discarded during cardiac surgery, the researchers believe there may be some similar cells in the adult heart. “The cardiac muscle cells formed were totally mature and had the complete array of function that one would expect in completely differentiated heart tissues,” said co-author Dr. Jason Lam in a statement.

In a commentary on the research, Dr. Christine Mummery of the Institute of the Netherlands in Utrecht said the research suggests the heart has some regenerative capacity.

“The heart was thought to lack the capacity to regenerate after injury. But the identification of cells that can divide and mature into heart muscle suggests that the heart has repair mechanisms after all,” she said.