How does Starling's law of the heart relate to stroke volume?

Starling's law of the heart, also known as the Frank-Starling mechanism, describes the relationship between the stretch of heart muscle fibers and the force of contraction they generate. This law indicates that the stroke volume, or the amount of blood ejected with each heartbeat, increases as the end-diastolic volume rises.

When more blood fills the ventricles during diastole (the heart's relaxation phase), the muscle fibers of the heart are stretched more. This stretching results in a more powerful contraction due to optimal alignment of the actin and myosin filaments in the cardiac muscle cells. As a result, the heart can eject more blood, leading to an increased stroke volume.

This direct relationship becomes particularly significant in the physiological context where the heart continuously adjusts its output according to the volume of blood returning to it, ensuring that more blood is pumped when necessary, such as during physical activity or in response to increased venous return.