What is preload?

What is preload?

• A. The initial stretching of the cardiac muscle fibers prior to contraction.
• B. The resistance the heart must overcome to eject blood during systole.
• C. The amount of blood remaining in the ventricles after contraction.
• D. The electrical activity of the heart.

Answer: (A)

Preload is the initial stretch of the ventricular muscle fibers just before they contract. It depends on how much blood fills the ventricles during diastole (the end-diastolic volume) and the pressure with which the ventricle fills, which is largely a result of venous return. This stretch sets the starting length of the cardiac muscle fibers and influences the strength of the subsequent contraction through the Frank-Starling mechanism: more preload means the fibers are stretched closer to their optimal length, so the heart can pump more vigorously and increase stroke volume, within physiological limits. Preload is different from afterload, which is the pressure the ventricle must overcome to eject blood during systole; it is not about how much blood remains after contraction (that’s end-systolic volume) and it does not describe the electrical activity of the heart. Clinically, preload is reflected by filling pressures such as central venous pressure or LV end-diastolic volume. High preload indicates more filling (often fluid overload), while low preload suggests underfilling (dehydration or hemorrhage). So preload is the initial stretching of the cardiac muscle fibers prior to contraction.

Preload is the initial stretch of the ventricular muscle fibers just before they contract. It depends on how much blood fills the ventricles during diastole (the end-diastolic volume) and the pressure with which the ventricle fills, which is largely a result of venous return.

This stretch sets the starting length of the cardiac muscle fibers and influences the strength of the subsequent contraction through the Frank-Starling mechanism: more preload means the fibers are stretched closer to their optimal length, so the heart can pump more vigorously and increase stroke volume, within physiological limits.

Preload is different from afterload, which is the pressure the ventricle must overcome to eject blood during systole; it is not about how much blood remains after contraction (that’s end-systolic volume) and it does not describe the electrical activity of the heart.

Clinically, preload is reflected by filling pressures such as central venous pressure or LV end-diastolic volume. High preload indicates more filling (often fluid overload), while low preload suggests underfilling (dehydration or hemorrhage).

So preload is the initial stretching of the cardiac muscle fibers prior to contraction.