The new technology, successfully tested in mice, opens up the possibility of hearts healing themselves.
Treatment consists of a single injection of the messenger RNA molecule, which contains the code for making a growth protein.
Mice given the molecule within 48 hours of a heart attack showed markedly improved survival and heart function. The effect appeared to be long-lasting.
Study leader Professor Kenneth Chien, from the Karolinska Institute in Sweden, said: "This is the beginning of using the heart as a factory to produce growth factors for specific families of cardiovascular stem cells, and suggests that it may be possible to generate new heart parts without delivering any new cells to the heart itself."