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

By two days we saw tiny, microscopic contractions, and by seven to eight days there were contractions large enough to see with the naked eye," she said. The tiny hearts could pump liquid at about one-fourth the rate of a normal fetal rat´s heart.

"Obviously we have a long way to go," Taylor said. But the long-term hope, she said, is that a similar process could work with either human hearts from cadavers or pig hearts, with their cells stripped off and replaced by cells from the person needing a heart transplant to avoid rejection.

The next step is to take a pig heart, strip away the cells and repopulate it with cells from a pig to see if it will work in the larger heart.

Dr. John Mayer Jr., a heart specialist and researcher at Children´s Hospital in Boston, said the report was an "important paper that advances the ball down the road." But, he added, "It´s pretty long road."

Mayer, who was not part of Taylor´s research team, noted that this was done in a small animal and it remains to be seen whether the same can be done in larger ones. He also wondered whether blood would flow freely, without clotting, through the reconstructed blood vessels.

"I think this is an important contribution, with more work to be done," Mayer said in a telephone interview.

In her research paper, Taylor also reports that the researchers are working on reseeding cells into other organs, including lungs, liver and kidneys.

The research was funded by the University of Minnesota and the Medtronic Foundation, the charitable arm of a medical company that makes heart devices such as stents and defibrillators