In 1602 Harvey returned to London and began work as a doctor at St. Bartholomew's Hospital and in 1615 he was appointed Lumleian Lecturer at the College of Physicians.
Harvey became court physician to James I in 1618. Ten years later Harvey published On the Motion of the Heart and the Blood in Animals. In the book Harvey explained that after examining the heart and blood vessels of mammals he believed that the blood in the veins must flow only towards the heart. He also calculated the amount of blood that left the heart at each beat.
William Harvey died in 1657.