Even though heart attacks may not be deadly, they can leave your ticker damaged. The reason: they occur when blood flow to a section of heart muscle becomes blocked. If the flow of blood isn't restored quickly, a section of the heart muscle becomes damaged from the lack of oxygen and begins to die, weakening its ability to pump blood.

Researchers have long wondered whether such damage could be reversed, that is, whether hobbled heart muscle cells could regenerate — potentially affecting the ability of scientists to hatch ways to repopulate damaged heart tissue. A study in Science today confirms that some heart muscle cells do, in fact, regenerate slowly over the course of a person's lifetime. Scientists from the Karolinska Institute in Sweden report that in early adulthood, we're continually renewing about 1 percent of our heart cells a year; that regeneration slows down, but it still occurs in old age, with a little less than half of 1 percent of cells regenerating at age 75. All told, we've renewed about 40 percent of our heart cells by age 70, neuroscientist Jonas Frisén told Science in a podcast.

Those results suggest that heart cells could, in fact, be nudged to regenerate or artificially replaced through cell transplants, according to an editorial accompanying the study. "Even though cardiomyocyte (heart muscle cell) turnover is low in the adult heart, the fact that it occurs at all suggests that it can potentially be therapeutically exploited," write Charles Murray, co-director of the University of Washington's Institute for Stem Cell and Regenerative Medicine, and Richard Lee, an associate physician in cardiology at Brigham and Women's Hospital in Boston.

In this study, Frisén compared the age of heart cell DNA to chronological age in people who were alive during Cold War nuclear tests and would have been exposed to radioactive carbon-14. Because carbon-14 is stored in DNA strands, Frisén was able to use the isotope (whose levels have declined since above-ground nuclear test bans were implemented in the early 1960s) as a marker to calculate the rate at which cells turn over. We profiled Frisén's carbon dating technique in the November 2005 issue of Scientific American.

To learn more about how scientists might repair damaged heart tissue, check out our 2004 feature on rebuilding broken hearts.

Hear a 60-Second Science podcast on this study.

Image © iStockphoto/Mads Abildgaard