When the English physician William Harvey claimed in 1628 that the heart was responsible for pumping blood throughout the body, the medical community largely criticized him. Today, we know that his research laid the groundwork for our modern understanding of circulation and physiology.

Harvey (1578–1657) was a highly respected doctor in London and the personal physician of King James I (1566–1625) and his son Charles I (1600–1649). In 1615, Harvey became a lecturer for the College of Physicians, where he often discussed his controversial theory. His notions about the role of the heart were quite a departure from the commonly accepted belief that blood’s movement through the body was caused by an innate pulsing in the arteries themselves. This traditional philosophy also held that there were two types of blood, venous and arterial, and that venous blood was produced in the liver and converted from food. It was assumed that, instead of circulating continuously, blood was simply absorbed by the body and new blood was constantly produced.

The culmination of Harvey’s research came with the publication of An Anatomical Essay Concerning the Movement of the Heart and the Blood in Animals, a report that explained how blood was propelled through the arteries by heartbeats. It argued that in animal experiments, the amount of blood forced out of the heart in an hour far exceeded the blood’s volume in the whole creature—thus suggesting that the blood must be circulating, otherwise the arteries would burst under pressure. Although he could not see the capillaries that branch out to nourish the body’s tissues and connect the arteries to the veins, Harvey proposed the existence of such tiny blood vessels, as well.

Harvey’s ideas were not trusted at the time, and his radical theories lost him many patients. But within his lifetime his ideas were eventually accepted, although they did not change common medical practices, such as bloodletting, for many years.

ADDITIONAL FACTS

  1. A second groundbreaking work published by Harvey in 1651, Essays on the Generation of Animals, is considered the basis for modern embryology.
  2. Harvey was able to witness the way a human heart pumps blood firsthand when he met a young man who had a gaping hole in his chest as a result of a childhood injury. The man wore a metal plate over the wound, but he could remove it to expose to Harvey and other observers his heart beating through the scar tissue.
  3. In one famous experiment, Harvey showed the existence and function of valves in the veins. He cut off circulation in a patient’s arm with a tourniquet, then tried to push the blood in the swollen veins away from or toward the heart. He was able to empty the veins in only one direction (toward the heart), showing that the valves allowed blood to flow only one way.