Heart, Law of the

(also Starling’s law), the law stating that the energy set free at each contraction of the heart is a function of the length of the heart’s muscle fibers. The energy of each contraction of the heart (systole) is directly proportional to the diastolic filling.

The law of the heart was established by the British physiologist E. Starling in studies conducted from 1912 to 1918 using heart-lung preparations. Starling found that the volume of blood pumped by the heart into the arteries at each systole increases in proportion to the increase in venous blood flow toward the heart. The intensified force of each contraction is associated with an increase in the volume of blood in the heart at the end of a diastole and with the resulting elongation of myocardial fibers.

Although the law of the heart does not entirely define heart function, it does elucidate one of the mechanisms involved in the heart’s ability to adapt to changes in the body. Specifically, the law establishes the basis for maintaining a relatively constant stroke volume in the arterial section of the cardiovascular system at the same time that vascular resistance is growing. This automatic mechanism is determined by the properties of the myocardium and participates in regulating both the heart and the entire cardiovascular system. It is controlled by neural and humoral influences.