This Tiny, Beating Heart Was Made From Stem Cells

They're only half a millimeter in diameter -- about a third the length of a pinhead -- but they're there, thumping away. Tiny, beating almost-hearts.

Scientists have grown the miniature organs, one of which you can see below, from human stem cells derived from skin tissue, and they're the first human heart chamber ever developed in vitro. The findings could someday help researchers determine how medications affect the hearts of developing fetuses, according to a study  published in the journal Nature Communications.

The tiny "heart" is actually a cardiac microchamber, which is basically a functional model of a human ventricle, that researchers hope will someday be used "to model aspects of early developing heart[s]," the paper reads. Stem cells were placed in a petri dish to grow, but were "coaxed" with oxygen plasma so they would turn into cardiac tissue, Popular Science notes . Twenty days later, the cells had developed into beating little models of a human organ.

The research is notable because it would allow scientists to use humanlike hearts in medical research rather than the rodent hearts currently used.

“We believe it is the first example illustrating the process of a developing human heart chamber in vitro,” Kevin Healy, a professor at University of California, Berkeley and co-author of the study, said in a press release . “This technology could help us quickly screen for drugs likely to generate cardiac birth defects, and guide decisions about which drugs are dangerous during pregnancy.” 

To test the efficacy of future trials, the researchers also grew some of the microchambers with an added drug called thalidomide in levels that would mimic the exposure a fetus gets during pregnancy. Thalidomide, which used to be prescribed to treat morning sickness, has been linked to birth defects , including abnormalities of the heart, the BBC notes.

The cardiac tissue exposed to the drug "significantly damaged the cardiac microchambers, generating chambers with smaller size, lower contractility and beat rates compared with controls."

Take a look at the stunning video below to see the little organs in action.