Cardiac stem cells derived from young hearts helped reverse the signs of aging when directly injected into the old hearts of elderly rats, a study published Monday in the European Heart Journal demonstrated.

The old rats appeared newly invigorated after receiving their injections. As hoped, the cardiac stem cells improved heart function yet also provided additional benefits. The rats’ fur fur, shaved for surgery, grew back more quickly than expected, and their chromosomal telomeres, which commonly shrink with age, lengthened.

The old rats receiving the cardiac stem cells also had increased stamina overall, exercising more than before the infusion.

“It’s extremely exciting,” said Dr. Eduardo Marbán, primary investigator on the research and director of the Cedars-Sinai Heart Institute. Witnessing “the systemic rejuvenating effects,” he said, “it’s kind of like an unexpected fountain of youth.”