Preload refers to what?

• A. The force of ventricular contraction
• B. The resistance to ventricular ejection of blood
• C. The amount of blood filling the ventricle at end-diastole
• D. The rate of atrial contraction

Answer: (C)

Preload is about how much the ventricle is filled with blood just before it contracts. This filling determines the initial stretch of the cardiac muscle fibers and is set by the amount of blood returning to the heart during diastole. In practice, preload corresponds to the end-diastolic volume (or pressure) — the amount of blood in the ventricle at the end of diastole. The more the ventricle is filled at end-diastole, the greater the preload, up to physiological limits, which helps determine the ensuing stroke volume via the Frank-Starling relationship.

The other options describe different concepts: the force of ventricular contraction is related to contractility, the resistance to ejection is afterload, and the rate of atrial contraction relates to heart rate or atrial systole.