This book presents a new interpretation of how and why the discovery of the circulation of the blood in animals was made. It has long been known that the English physician William Harvey (1578–1657) was a follower of Aristotle, but his most strikingly 'modern' and original discovery – of the circulation of the blood – resulted from Harvey following Aristotle's ancient programme of investigation into animals. This is a new reading of the most important discovery ever made in anatomy by one man and produces not only a radical re-reading of Harvey as anatomist, but also of Aristotle and his investigations of animals.