"It takes us now about an average I would say about two hours of manual work on the computer to manipulate the data in to generate the 3D model and the printer takes about, for a full size heart like this, it takes about 12 hours," said mechanical engineer Alex Krieger, the principal investigator for pediatric surgical innovation at the Children's National Medical Center. "A smaller heart maybe five, six hours.

Krieger says in one instance his team printed a model of the heart of a patient with stenosis, or narrowing of the passage between two heart chambers. The interventional cardiologist wanted to see exactly what kind of stent he should use, the size and length of it, and also the access path.

"So this model allowed him to really look at that in depth and plan, and prepare for the procedure better," he said.

The machine prints by spraying layers of plastic, one on top of the other, while the ultraviolet light immediately cures it before the next layer is sprayed. Krieger says the printer can be loaded with two different materials. Precise control of their ratio allows the printed model to feel very natural, with both hard and soft tissues.

Cardiologist Olivieri says doctors still have to learn a lot about the new procedure.

"It's a brand new field. These have only been possible for a wery little amount of time and I don't think we even know the full capability of what we're going to be... what they're going to be used for," she said. "We're kind of talking about a technology that went going from feasible to kind of usable and we're right in that middle ground right now.