Leonardo da Vinci returns to Milan again. He will never return to Florence. He likes Milan better: it lacks the hated Michelangelo, his brothers aren’t there to sue him, and there’s a vertical power structure where he’s in direct contact with the highest levels, rather than the chaotic Florentine Republic. In Milan, shortly after his arrival, at the Santa Maria Nuova hospital, he meets an elderly man who claims to be a hundred years old. A few hours later, the man dies, and Leonardo obtains permission to dissect his body. This launched his second cycle of anatomical studies on man, which lasted from 1508 to 1513. Leonardo was thus the first to describe arteriosclerosis in detail, among the first to recognize the heart (rather than the liver) as the center of the blood circulation system, the first to recognize the heart as a simple muscle and not composed of specialized tissues, he corrected Galen in his belief that the heart has four ventricles and not two, discovered that the two upper ventricles open at different times than the two lower ones, and, his most incredible discovery, understood how the aortic valves close: through the vortices of blood entering the heart. He made this last discovery by creating a plaster cast of a heart and a glass model on the cast, then ran pressurized water through it and filled it with grass seeds to trace its movement. It would take another 450 years to realize that Leonardo was right. In the 1960s, a team of researchers led by Brian Bellhouse of Oxford used X-rays to (re)discover the vortices that close the aortic valves. In 2014, another team from Oxford used magnetic resonance imaging to image the aortic valves in real time. Of all Leonardo’s discoveries, this is perhaps the most extraordinary. But Leonardo never published anything. Upon his death, he left Francesco Melzi only a stack of written and drawn papers. Modern anatomy, unaware of Leonardo, would only be born 25 years after the master’s death, with Andreas Vesalius. Leonardo’s discoveries, in the years and centuries to come, will have to be rediscovered.
