In the body, carbon-14 in the diet gets into the DNA of new cells and stays unchanged for the life of the cell. Because the level of carbon-14 in the atmosphere falls each year, the amount of carbon-14 in the DNA can serve to indicate the cell’s birth date, Dr. Frisen found.

Four years ago he used his new method to assess the turnover rate of various tissues in the body, concluding that the average age of the cells in an adult’s body might be as young as 7 to 10 years. But there is a wide range of ages  from the rapidly turning over cells of the blood and gut to the mostly permanent cells of the brain.

Image Dr. Jonas Frisén of the Karolinska Institute in Stockholm. Credit... Camilla Svensk

Dr. Frisen has successfully applied his method to the heart muscle cells, but had to navigate a series of technical obstacles created by the special behavior of the cells. Many have two nuclei, instead of the usual one, and within these double nuclei the DNA may be duplicated again. “I was really impressed at the level of rigor they put into this analysis,” Dr. Murry said, calling it a “scientific tour de force.”

The finding that heart muscle cells do regenerate, though at a considerably slower rate than Dr. Anversa predicted, is a “reasonable conclusion to a hotly contested issue,” Dr. Murry said. “Anversa went out on a limb, and I think he was partly right.”

Dr. Loren Field, a heart expert at the Indiana University School of Medicine, said he had found that heart muscle cells regenerated in mice at the same rate that Dr. Frisen had found in people. Despite the controversy created by Dr. Anversa’s claims, there has long been agreement that there is a low but detectable rate of cell renewal in the heart, Dr. Field said. The goal now, in his view, is “to try to tickle the system to enhance it.”

Dr. Anversa, for his part, said he was “ecstatic” at Dr. Frisen’s confirmation of his view that the heart could generate new muscle cells, but suggested that the new measurements might have underestimated the rate at which new cells are formed. Since heart muscle cells contract 70 times a minute, they seem likely to need renewing more often than Dr. Frisen’s measurements suggest, he said. “Now let’s discuss the magnitude of the process, and that will let us think about how we can apply this concept to heart failure,” Dr. Anversa said.