Tiny molecules called microRNAs may someday help heart attack survivors recover.

Earlier this year, it was shown that some of the damage caused by a heart attack could be repaired by giving patients an injection of their own stem cells. Now, researchers from Duke University have done the same by injecting tiny molecules of RNA known as microRNAs.
Because microRNAs are so small, they can be made synthetically, which makes them a much better candidate for therapy than stem cells, which much first be isolated from a patient and then grown up in the laboratory.
It wasn't long ago that scar tissue was thought to be permanent. Though that's now known not to be true, the science of turning scar tissue back into healthy tissue is still in its infancy.
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Much of the damage from a heart attack comes from the death of heart muscle tissue, which is replaced by scar tissue. Scar tissue is something like a patch; it's never as functional as the tissue it replaces. In the heart, scar tissue can't contract and beat like heart muscle tissue can. And with less muscle, the heart can no longer pump blood as well as it did before the heart attack. But it might if the scar tissue could be turned back into muscle tissue. Which is what the Duke scientists appear to have accomplished in mice.