Physiology
As the heart fills with more blood than usual, the force of cardiac muscular contractions increases. This is a result of an increase in the load experienced by each muscle fiber due to the extra blood load entering the heart. The stretching of the muscle fibers augments cardiac muscle contraction by increasing the affinity of troponin C for calcium, causing a greater number of actin-myosin cross-bridges to form within the muscle fibers. The force that any single cardiac muscle fiber generates is proportional to the initial sarcomere length (known as preload), and the stretch on the individual fibers is related to the End Diastolic Volume of the left and right ventricles.
In the human heart, maximal force is generated with an initial sarcomere length of 2.2 micrometers, a length which is rarely exceeded in the normal heart. Initial lengths larger or smaller than this optimal value will decrease the force the muscle can achieve. For larger sarcomere lengths, this is the result of less overlap of the thin and thick filaments; for smaller sarcomere lengths, the cause is the decreased sensitivity for calcium by the myofilaments.
Read more about this topic: Frank–Starling Law Of The Heart
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