What did people believe about blood flow before William Harvey’s discovery?

Before William Harvey’s discovery, the prevailing belief was that the body contained two separate, non-circulating blood systems. This view, largely influenced by the ancient physician Galen, held that blood was continuously consumed by the body at the same rate it was produced.12

The two systems were described as follows:
* Venous system: Believed to carry purple, "nutritive" blood from the liver to distribute nourishment throughout the body.12
* Arterial system: Believed to carry scarlet, "vital" blood from the heart and lungs to distribute a life-giving principle.12

Additionally, it was thought that the active phase of the heartbeat involved the heart expanding to draw blood into itself, rather than contracting to pump it out. Because the capillaries were unknown, the idea of a continuous, closed circulatory system was not understood. While some earlier scholars, such as Ibn al-Nafis, had suggested a "lesser circulation" between the heart and lungs, the concept of blood circulating throughout the entire body remained unrecognized until Harvey’s work.1