What principle does the Frank Starling Law describe?

The Frank-Starling Law describes the relationship between end-diastolic volume (EDV) and stroke volume (SV), highlighting how the volume of blood in the ventricles at the end of diastole influences the amount of blood ejected during systole. According to this principle, when the ventricle is filled with more blood, it stretches the cardiac muscle fibers, leading to a more forceful contraction due to the optimal overlap of actin and myosin filaments within the myocardium. This means that as the end-diastolic volume increases, the stroke volume also increases, up to a certain point.

This relationship is critical in understanding how the heart adjusts its output in response to varying volumes of incoming blood, which is essential for maintaining effective circulation, particularly during physical activity when the body demands more oxygen and nutrients. Thus, option B accurately represents the fundamental concept of the Frank-Starling Law.