Growing hearts: Doris Taylor (above) and her colleague Stefan Kren are creating live bioartificial hearts. Credit: Jonathan Chapman

In Doris Taylor's cell- and molecular-­biology lab at the University of ­Minnesota, a small pink heart beats in a glass chamber amid a complex of tubes. With each twitch, the heart's bottom tip traces a small curve in space, and pink nutrient solution flows out through the aorta. Remarkably, this living heart was grown in the lab.

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