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RANDOLPH E. SCHMID

Researchers seeking new treatments for heart disease managed to grow a rat heart in the lab and start it beating.

we've hopefully opened a new door in the notion that we can build these tissues and one day provide options for patients with end-stage disease," said Dr. Doris Taylor, director of the Center for Cardiovascular Repair at the University of Minnesota.

her team began by trying to determine if it were possible to transplant rat heart cells. They took the hearts from eight newborn rats and removed all the cells. Left behind was a gelatin-like matrix shaped like a heart and containing conduits where the blood vessels had been. Scientists then injected cells back into this scaffold -- muscle cells and endothelial cells, which line blood vessels.

The muscle cells covered the matrix walls and lined up together, while the endothelial cells found their way inside to coat the blood vessels, she said. Then the hearts were stimulated electrically