Preload is defined as what?

• A. The degree of stretch of the cardiac muscle fibers at the end of diastole.
• B. The pressure the ventricles must overcome to eject blood.
• C. The strength of contraction of the heart muscle.
• D. The volume of blood in the ventricles at the end of systole.

Answer: (A)

Preload is the degree of stretch of the ventricular muscle fibers at the end of diastole, right before the heart contracts. This stretch reflects how much the ventricles have filled with blood (end-diastolic volume) and is influenced by venous return. The stronger contraction that follows—up to a limit—depends on this initial fiber length (the length-tension relationship described by the Frank-Starling mechanism). It’s not about the pressure the ventricle must overcome to eject blood (that’s afterload), not about the intrinsic strength of contraction (contractility), and not the volume left after systole (end-systolic volume). So the correct description is the stretch of the ventricles at the end of diastole.