Experts have long believed the adult heart is incapable of repairing itself, since heart muscle cells stop dividing once they’re fully formed. Now, a U.S. team says they’ve found a way to coax cells to divide again, which could provide a way to regenerate healthy tissue. In a study performed on rats and mice, Boston-based researchers tested different molecules to spur cell division in heart cells. A growth factor called neuregulin1 (NRG1) was shown to speed up the process significantly: when injected into adult mice who’d suffered a heart attach, it promoted heart muscle repair and improved overall function of the organ. This could be used to treat heart attack patients, people with heart failure, and children with congenital heart defects, the BBC reports, as well as offering an alternative to stem cell therapy, which is still untested and has the risk of side effects. The next step will be testing the technique in pigs.