Ideas often burst into our conscience and temporarily fuel us until we let them remain just that -- an idea, abstract and intangible. Seventeen-year-old Catherine Wong had one of these ideas. But instead of letting it remain conceptual, she built what she imagined, and then she entered NPR's "Big Idea" contest. She built a functioning and low-cost electrocardiogram that transmits heart rhythms through cell phones for people with no access to health care. What can you do with your ideas?