Which measurement best reflects preload?

• A. End-diastolic volume.
• B. End-systolic volume.
• C. Mean arterial pressure.
• D. Ejection fraction.

Answer: (A)

Preload is the initial stretch of the ventricular muscle fibers at the end of filling, determined by how much blood returns to and fills the ventricle before it contracts. End-diastolic volume directly measures how much blood is in the ventricle at that moment, so it best reflects how much the ventricle was filled and, thus, the preload. End-systolic volume comes after contraction and reflects what remains, more about afterload and contractility than filling. Mean arterial pressure indicates systemic pressure and influences venous return indirectly, but it doesn’t quantify the filling volume. Ejection fraction looks at how much of the filled volume is ejected and is a measure of contractile performance, not filling level. So end-diastolic volume is the most direct indicator of preload.