What evidence did William Harvey use to argue that the heart pumps blood?

William Harvey provided several lines of evidence to demonstrate that the heart functions as a pump to circulate blood throughout the body:

• Quantitative Analysis: Harvey estimated the volume of the heart's ventricles and the rate of the heartbeat. He demonstrated that the heart pumps a volume of blood per minute that far exceeds what the body could possibly produce or consume, necessitating that the blood must circulate within a closed system.1
• Venous Valves: Harvey observed that the valves inside veins are oriented to allow blood flow in only one direction. By showing these valves are cardiocentrically oriented—inhibiting flow away from the heart rather than merely preventing pooling due to gravity—he provided evidence of a directional, continuous flow.1
• Observation of the Heartbeat: Through the study of various animals, particularly those with slow heartbeats, Harvey corrected the prevailing belief that the heart's active phase involved drawing blood in. He observed that during contraction, the heart decreases its internal volume, forcefully expelling blood.1

These findings, detailed in his work Anatomical Exercise on the Motion of the Heart and Blood in Animals, fundamentally shifted the understanding of human physiology.12