At any moment, about 3,000 people in the United States alone are waiting for a replacement heart – one whose tissue is compatible with the recipient. Artificial hearts are the solution, but designs so far have been clunky and fraught with problems. Now medical engineers at ETH Zurich, a Swiss science and technology university, have 3D-printed a silicone heart that closely matches the shape and weight of original equipment. The heart has two chambers separated by a smaller compartment. The heart pumps as the compartment is inflated with air and then deflates. The new heart isn’t ready for installation; it wears out after 3,000 beats, which is less than an hour’s use in a person. But developers are content they’ve shown a new path to new hearts.