In 2017, Nishith Khandwala was a Stanford computer science student with an idea—that you could take existing radiology scans, and use AI to check them at scale and detect heart disease and heart attack risk early. For years, he and classmate David Eng developed the project—but even when it worked, they hit a wall. Hospitals more or less shooed them away, and it seemed like it might be time to move on. But in 2020, Khandwala’s father had a heart attack. “The cardiologist told us: ‘There was actua...