In 1929, a young German cardiologist named Werner Forssmann threaded a rubber catheter through his own arm vein and into his beating heart — then walked to the X-ray department to photograph his proof. His colleagues called it madness, his hospital fired him, and the medical establishment buried the idea for a decade. Today, cardiac catheterization saves millions of lives a year, and the story of how it got there is equal parts recklessness, institutional cowardice, and the stubborn physics of blood.