What does stroke volume measure in the heart?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

In the context of the circulatory system, stroke volume measures the amount of blood that is pumped by each ventricle of the heart with every individual heartbeat.1

It is a key determinant of cardiac output, which is calculated by multiplying the stroke volume by the heart rate. Stroke volume itself is primarily influenced by three factors:

Preload: The degree of ventricular filling before contraction, which stretches the heart muscle and increases the force of contraction.1
Afterload: The resistance the ventricle must overcome to eject blood into the arteries; higher resistance generally reduces the volume ejected.1
Contractility: The intrinsic strength of the heart muscle's contraction, independent of filling; stronger contractility increases the stroke volume.1