The heart was created using a 3D-printed method that lets the researchers make a complex inner structure while still using soft, flexible material as its structure. The whole thing is basically one single part (a “monoblock”), so there’s no need to worry about how different internal mechanisms fit together — except at the input and output ports, where blood would come and go.
In tests the heart worked quite well, pushing a blood-like fluid along against body-like pressures. There is, of course, a catch.
This heart is a proof of concept, not built for actual implantation — so the materials they made it from don’t last more than a few thousands beats. That’s about half an hour, depending on your heart rate