According to the Frank-Sterling Law, what happens to contractility with increased volume?

The Frank-Starling Law describes the relationship between the volume of blood filling the heart (preload) and the force of contraction (contractility) of the cardiac muscle. According to this law, as the volume of blood in the ventricles increases, there is an increase in the length of the cardiac muscle fibers during diastole. This increased fiber length leads to a more forceful contraction during systole due to enhanced interaction between actin and myosin filaments.

When additional blood enters the heart, this results in a higher end-diastolic volume, which stretches the cardiac muscle fibers. The greater stretch leads to an increased force of contraction, thereby improving contractility. This physiological mechanism ensures that the heart can pump out more blood to meet the body's demands, particularly under conditions like exercise or increased metabolic activity.

This principle is fundamental to understanding cardiac function and the heart's ability to adapt to varying volumes of blood, which is crucial in clinical settings for evaluating heart performance and managing cardiovascular conditions.