Discovery of Pulmonary Circulation

Writing in the thirteenth century, the Damascene physician Ibn al-Nafis rejected the long accepted Galenic view that blood passes between the two sides of the heart through invisible pores in the septum. In his commentary on Avicenna's Canon of Medicine, composed when he was still in his twenties, he argued instead that blood travels from the right chamber of the heart through the lungs, where it mixes with air, before returning to the left chamber, describing what is now called the pulmonary circulation. His account anticipated by roughly three and a half centuries the fuller description of the whole circulatory system that William Harvey published in the seventeenth century, and historians of science regard Ibn al-Nafis as the first to break with Galen's authority on this point.