What does the Frank-Starling principle describe?

The Frank-Starling principle describes the relationship between the degree of stretch of the cardiac muscle fibers (preload) and the resulting strength of contraction (ejection fraction) of the heart. Essentially, this principle states that within certain limits, the more the heart is filled with blood (increased preload), the greater the force of contraction during systole. This allows the heart to adjust its pumping efficiency based on the volume of blood returning to it.

When preload is increased, the myocardial fibers are stretched more, leading to a more powerful contraction and a higher ejection fraction. This is a critical mechanism that enables the heart to respond dynamically to changes in blood volume and demands in circulation, effectively optimizing cardiac output.

Understanding this principle is fundamental in situations like heart failure or fluid overload, where the heart's ability to contract and the effectiveness of its pumping action become critical points of concern.