Amanda Randles, an assistant professor of biomedical engineering at Duke University, is building software that simulates blood flowing throughout the human body in a model based on medical images of a particular person. The code base is called “HARVEY,” after William Harvey, a 17th-century surgeon who first described the circulatory system. The software requires a supercomputer to crunch calculations on the fluid dynamics of millions of blood cells as they move through the blood vessels. Randles has other plans for her fluid-dynamic model of the circulatory system. Next up: scanning newborns with heart problems to guide surgeons and predicting how cancer cells move through the body.