- The Frank-Starling law describes the intrinsic ability of the heart to adjust its pumping function in response to changes in venous return or ventricular filling pressure.
- According to this law, an increase in the volume of blood filling the heart (end-diastolic volume) leads to a greater stretch of the ventricular muscle fibers.
- This stretch results in a more forceful contraction, thereby increasing the stroke volume — the amount of blood ejected with each heartbeat.

- In simple terms, the Frank-Starling mechanism ensures that the heart automatically balances its output with the amount of blood returning to it.
- This relationship is crucial for maintaining cardiac output under varying physiological conditions without relying solely on external regulatory systems.

Therefore, the law primarily illustrates the relationship between ventricular filling pressure (or preload) and stroke volume. It does not directly address heart rate, afterload, myocardial contractility, or arterial pressures.

Reference: Guyton and Hall Textbook of Medical Physiology, 13th Edition, Chapter 14, Page 164