Scientists in the United States and Australia used human embryonic stem cells to cultivate billions of heart muscle cells which they transplanted into injured macaque hearts, according to research findings published in the journal Nature.
"The human grafts remuscularised about 40 percent of the damaged region," of the hearts of monkeys used in the experiment, study co-author Charles Murry of the University of Washington's Center for Cardiovascular Biology, told AFP.
"We showed that the human heart muscle is fed by blood vessels from the heart's native circulation. Importantly, we find that the human heart muscle integrated with the monkey's heart and beat in synchrony, up to 240 beats per minute."
Embryonic stem cells -- neutral, primitive cells that can develop into most of the specialised tissue cells of the body -- are viewed as a potential source for rebuilding organs damaged by disease or accident.
"The study represents an important step towards the possibility of cardiac muscle cell transplantation as a viable clinical therapy for heart failure," said a Nature summary.
Murry said this was the most human heart muscle that any team has managed to grow in a damaged heart.
Monkeys are the closest models of human heart disease, and he said there was "no reason to think" the technique would not work in humans.
However, the muscle grafts caused rhythm disturbances in the monkeys -- a complication that needs to be fixed.
"I do think we are getting close to being ready to try this therapy in human patients in carefully controlled clinical trials," Murry said.