The Frank-Starling Law

The Frank-Starling Law (also known as the heart law or heart preload law) is a physiological principle describing one of the local myogenic mechanisms that regulate heart function. This law states that the strength of the heart’s contractions is directly related to the extent of stretching of its muscle fibers. The greater the venous return to the heart during diastole (the heart’s relaxation phase), the more the cardiac muscle fibers stretch, leading to a stronger contraction during systole (the heart’s pumping phase). This law was independently discovered by the English physiologist Ernest Starling and the German physiologist Otto Frank.

An increase in heart load (for example, due to regular muscle activity) enhances the synthesis of contractile proteins in the myocardium (heart muscle) and the structures supporting their function. This leads to what is known as working (physiological) hypertrophy of the myocardium, commonly observed in athletes who train to improve their cardiorespiratory endurance.