Before new drugs can be used on humans, they need to go through a rigorous regime of testing on animals, artificial models or both, but results don't often carry across to humans completely. Now researchers have developed a technique to create more accurate models, by effectively turning rat hearts into miniature human hearts.

You could almost cobble together an entire doll-sized body from all the individual mini organs that have been developed over the years. Mini-kidneys, lungs, and livers are often grown from stem cells to test new drugs or study diseases, with the eventual goal of growing full-size replacement organs for transplants. Mini-brains have also proven themselves useful models of neurological function.

To "humanize" rat hearts, the researchers first removed the organ from the animals and subjected it to a process called 4-Flow cannulation. Basically, that allows specialized fluids to be introduced into the aorta, arteries and veins of a heart, while maintaining normal flow and full circulation. These fluids are designed to strip the rat cells right out of there, leaving the lining matrix behind to keep the overall structure intact. Human cells can then be introduced and they'll cling to the matrix, replacing the lost rat cells and effectively creating a mini human heart.

The researchers plan to use this technique to develop human heart models for testing new drugs and treatments for safety and efficacy, which saves the trouble and inaccuracy of using animal models.

The research was recently presented at the American Heart Association's Basic Cardiovascular Sciences 2017 Scientific Sessions conference.