Right now, there are 4,186 people waiting for a heart transplant in the U.S., but with a huge donor shortage not all of these patients are likely to survive. Growing transplantable hearts in a laboratory has been a long-standing dream within the medical community, and a study in the journal Circulation Research has moved it one step closer to reality: A team of researchers have successfully grown a beating human heart in the laboratory using stem cells.

According to the journal, the scientists took 73 donor hearts deemed unfit for transplantation, stripped away cells on those hearts and replaced them with skin cells that — using messenger RNA — had been turned into pluripotent stem cells, the kinds of cells that can be specialized to any part of the human body. After causing the stem cells to develop into two types of cardiac cells, the researchers then mimicked the environment a human heart would typically grow within and infused the cardiac cells with a nutrient solution that facilitated growth.

After two weeks, they shocked the hearts with electricity, and lo and behold, the hearts began beating. The tissue inside appeared to be well-structured and functional. Popular Science compared the growth of the heart as "building a house with the frame already constructed." 

Ultimately, the researchers aim to grow an entire human heart that is capable of being transplanted. 

While this isn’t the first time heart tissue has been grown in the lab, it’s the closest researchers have come to their end goal: Growing an entire working human heart. But the researchers admit that they’re not quite ready to do that. They are next planning to improve their yield of pluripotent stem cells (a whole heart would take tens of billions, one researcher said in a press release), find a way to help the cells mature more quickly, and perfecting the body-like conditions in which the heart develops. In the end, the researchers hope that they can create individualized hearts for their patients so that transplant rejection will no longer be a likely side effect.


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