Mackenzie Tannhauser doesn't take any of life's milestones for granted. Graduate high school. Go away to college. Earn a biomedical engineering degree. Start a STEM career. Travel to 20 countries. She has done it all over the last 11 years, but there was a time when Tannhauser wondered if she ever could — or would. When she was 8 years old, Tannhauser found herself exhausted, sitting on the sidelines during soccer. That year, she was diagnosed with an irregular heart rhythm. Her condition worsened despite more than 10 surgeries over the following five years. Eventually, she was put on the heart transplant list.