[The following is an exact transcript of this podcast.]

The heart-stopping news from Stockholm is that the heart never stops—growing, that is. Because researchers have shown that the human heart continues to produce muscle cells, even in adults.

Scientists have long debated whether the heart was capable of regeneration. They could make heart cells divide in a culture dish. But no one knew whether the cells could do the same in a living organism.

To find out, the Swedish scientists literally took advantage of fallout from the Cold War. The testing of nuclear weapons in the 1950s spewed a lot of radioactive carbon 14 into the air. That C-14 then got incorporated into the cells of every plant and animal on earth. When testing was banned in the ‘60s, C-14 levels dropped.

Those changing levels of radioactive carbon could be used to estimate when individual cells in the body, and in the heart, arose. Using this C-14 dating, the scientists found that a 25-year-old replaces about 1 percent of his heart cells a year, and a 75-year-old about half that, data published in the journal Science. The turnover is a tad slow but it does offer hope that damaged hearts might someday be made to mend themselves.

—Karen Hopkin

For more about this research, go to "Heart cells found to regenerate"