Who discovered blood circulation, challenging the medical theories of the time?

William Harvey

William Harvey, in his 1628 work "Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus," was the first to correctly describe the blood circulation system, demonstrating how the heart pumps blood throughout the body in a closed circuit. This discovery challenged the medical beliefs of the time, which were based on the theories of Galen. Harvey's work laid the foundations of modern physiology and transformed our understanding of how the human body functions, highlighting the importance of observation and experimentation in the medical field.