Ibn an-Nafis (or Ibn al-Nafis) (c. 1213–1288)

Syrian physician. He practised medicine at Cairo, Egypt, where he was dean of the Nasiri Hospital. Ibn an-Nafis was the first to explain pulmonary circulation (the circulation of the blood through the lungs for the purpose of oxygenation) correctly. He presented his discovery to the public in 1242, and included it in his 1286 commentary on the anatomy of Avicenna's Canon Medicinae. His work, probably unknown to his contemporaries in Europe, was later lost and only rediscovered in 1924.

Ibn an-Nafis's findings challenged the theories of Galen, a Greek physician of the 2nd century AD whose ideas were considered infallible by the Roman Catholic church. Galen believed that blood passed from the right to the left side of the heart through holes in the septum (dividing wall) between the chambers. Although Islamic law forbade dissection of the human body, Ibn an-Nafis correctly deduced that blood passed from the right to the left by way of the lungs. European doctors were probably unaware of Ibn an-Nafis's work but it is likely that his ideas would have proved unacceptable; apart from European prejudice against Muslim physicians, the Catholic church would have regarded anyone who disputed Galen's theories as heretical. Galen's explanation of blood flow was believed in Europe until the Flemish anatomist Andreas Vesalius proved it incorrect in the 17th century.