MINNEAPOLIS - When Karlie Gause was a 20 year old college student, radiation shrunk a giant tumor in her chest. But what saved her life damaged her heart, and she struggled with breathing and fatigue. [(I had) really no energy," Gause said. [The ability to get up and down stairs was not there." Karlie needed a new heart valve, but open heart surgery was risky. So doctors instead used a method called TAVR (Transcatheter Aortic Valve Replacement) threading the new valve through a catheter and into Karlie's heart. [With this procedure, you don't have much room for error," said Dr. Greg Helmer, a University of Minnesota Cardiologist. [So you want to give it your best shot each time, and you have one time." That's why surgeons wanted to test the valve first, making sure they used the right size and put it in the right position. So using a 3D printer, University of Minnesota researchers made an exact replica of Karlie's heart, letting doctors try lots of variations on the plastic model before they started surgery. [You can implant the valve a little higher or a little lower or right where you think it should be," Helmer said. [So we then did different testing of different valves at different locations." Those tests meant a flawless operation. For surgeons, 3D printing is a new way to treat at risk patients, and for Karlie, it means a new start. [I thought it was going to be great and it was," she said. [Really what it did was change my mindset. It made me more hopeful."