How did William Harvey demonstrate that blood circulates through the body?

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William Harvey demonstrated that blood circulates through the body by challenging the prevailing belief that blood was consumed by the body at the same rate it was produced. In his seminal work, Anatomical Exercise on the Motion of the Heart and Blood in Animals, he utilized two primary lines of evidence.1

First, Harvey analyzed the venous valves. He observed that these flaps are oriented to allow blood flow in only one direction, specifically toward the heart, rather than merely preventing pooling due to gravity.1

Second, Harvey performed a quantitative experiment regarding the heartbeat. By estimating the volume of the ventricles and the rate of heartbeats, he calculated that the heart pumps more blood per minute than the body could possibly produce or consume. He concluded that the heart acts as an organic pump that expels blood with force, necessitating a continuous, closed circulatory system where blood is recycled rather than replaced.1