EAST LANSING, Mich. (Michigan News Source) — This Christmas, Michigan State University has a heart that is thousands of times too small. But unlike the Grinch’s heart, this heart may help discover cures for elusive heart diseases.

Tiny heart, irregular rhythm.

MSU researchers have developed a miniature heart model the size of a lentil with the capacity to simulate atrial fibrillation, a heart disorder which causes irregular heartbeat and hasn’t had any new treatments in the past 30 years, according to a press release from the university.

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Most knowledge about human heart diseases is based on animal heart models, said the release, which often can’t accurately replicate the structure or cellular environment of the human heart. Researchers are now turning to heart organoids, miniature heart models grown from stem cells, to model diseases.

A new immune system, too.

According to a paper published in Cell Stem Cell, MSU’s heart organoid has chambers, arteries, veins, and capillaries, just like a real heart. A person can even see it beating without the help of a microscope. But the real breakthrough in this organoid is its new immune system.

Aitor Aguirre, associate professor of biomedical engineering, and his team at MSU’s Institute for Quantitative Health Science and Engineering successfully added special immune cells called macrophages to their heart organoid, something which has not yet been done before.

These immune cells caused inflammation in the organoid, resulting in an irregular heartbeat which mimicked the disease atrial fibrillation. The researchers then added an anti-inflammatory drug and witnessed the organoid rhythm return to normal.

Aguirre said the addition of immune cells will help researchers develop more accurate treatments for atrial fibrillation.

Accelerate therapeutic developments.

“This new model can replicate a condition that is at the core of many people’s medical problems,” Aguirre said in the release. “It’s going to enable a lot of medical advances so patients can expect to see accelerated therapeutic developments, more drugs moving into the market, safer drugs and cheaper drugs, too, because companies are going to be able to develop more options.”