As an architect-engineer, Leonardo da Vinci was interested in the relationship between mechanics and human anatomy. He was particularly fascinated by the heart and the flow of blood. Da Vinci was the first to describe the heart as a muscle and a four-chambered organ. He also described the mechanics of blood flow through the chambers, with the atria contracting together and the ventricles relaxing together, and vice versa. Most impressive were his observations of the aortic valve. He utilized a self-constructed glass model of a bovine heart filled with grass seeds suspended in water. He observed vortices at the root of the aorta and correctly hypothesized that the vortices helped close the aortic valve. Because these drawings and notes were never published, this functioning of the valve remained unknown until 1968, when two Oxford engineers published a paper in Nature describing this mechanism, with their only reference being da Vinci’s illustrations and notes of the heart. Sources: http://ac.els-cdn.com/0003497591913712/1-s2.0-0003497591913712-main.pdf?_tid=1fd6a60c-f321-11e6-a0d5-00000aacb362&acdnat=1487123607_d89b02d75d9aff4411c0efe55fc1520a & http://www.bbc.com/culture/story/20130828-leonardo-da-vinci-the-anatomist Image source: https://leonardodavinci.stanford.edu/projects/anatomy/heart1.jpg and it is in public domain.