A brief history of the discovery of the circulation of blood in the human body.

The present article describes briefly the development of the theories regarding the circulation of blood in humans, from the time of Galen (second century C.E.) to the work of William Harvey (17th century C.E.).We shall summarize the views of Galen together with those of two prominent Iranian physicians of the Middle Ages (Razi and Ahwazi known in the West as Rhazes and Haly Abbas respectively) as well as that of Ibn-Nafis from Damascus (the discoverer of the pulmonary circulation) and the Spanish physician and cleric Michael Servetus and finally the definitive work of William Harvey, the English physician who described the mechanism of both the systemic and pulmonary circulation of blood in the human body.