Heart attacks strike some 800,000 people in the U.S annually. Because heart tissue cannot regenerate after an injury, the damage inflicted on the cardiac muscle worsens over time. Scientists report in this week's online issue of the Proceedings of the National Academy of Sciences that they have successfully cultured working heart cells from rats. The feat should aid efforts to engineer patches for broken hearts.

Conventional culture methods don't work for heart cells--they tend to lose their shape and stop functioning properly. In the new work, the researchers placed cardiac cells from a rat onto a polymer scaffold and immersed the setup in a nutrient bath. The team then applied electrical signals, which were designed to mimic a beating heart, to the growing cells. After eight days, single cells were transformed into functional heart tissue with structure similar to that of mature cardiac tissue samples. In addition, the cells expressed cardiac proteins and showed a seven-fold increase in the amount they could contract compared with cells cultured without electrical stimulation.

The next step for the research team is to build a section of cardiac tissue that is thick enough for clinical applications. "The greatest challenge," lead author Gordana Vunjak-Novakovic of the Massachusetts Institute of Technology says, "is to reproduce this with human cells, and test how all this works in the body."