The vast majority of cells in our bodies regenerate: our skin, stomach lining, red blood cells, bone cells, liver cells... the list goes on. But certain cells either do not regenerate at all, or take years to do so.

One of those cells is the heart muscle cell called cardiomyocyte. Starting at birth, they regenerate at just one percent a year and by the time we die, only half of our original heart muscle cells are replaced.

That's why damage from a heart attack is considered permanent. Within minutes, depending on where the blockage occurred, cardiomyocytes are either damaged or dead.

The heart can't produce replacement cells fast enough. Instead, scar tissue replaces muscle which compromises the heart's ability to pump blood. Scientists have been looking for a way to stop, slow or heal this damage, and they're making headway.

Researchers are focused on a small protein called Thymosin beta-4, or T-beta-4. When the heart develops inside a human embryo, T-beta-4 is expressed.

The protein encourages the growth of cardiomyocytes, and stimulates the growth of blood vessels. Could this protein be used somehow to heal a damaged heart?

Scientists have known the outer layer of the heart holds heart progenitor stem cells called epicardium-derived progenitor cells or EDPCs . They're usually dormant, but researchers found that mice given T-beta-4 seem to give the EDPCs a jump start.

The protein not only reduced the number of cardiomyocytes killed during a heart attack, but also prepared dormant progenitor cells to regenerate those that did die. The mice also show new blood vessel formation in the heart over the long term.

T-beta-4 is already in clinical trials and scientists hope within ten years, it'll be ready to help the millions of Americans who suffer heart attacks.