Which factor most directly increases preload?

• A. End-diastolic volume
• B. Systemic vascular resistance
• C. Venous return
• D. End-systolic volume

Answer: (C)

Preload is the stretch on the ventricles at the end of diastole, set by how much blood fills the ventricle. The factor that most directly increases preload is venous return, because more blood returning to the heart during diastole raises the ventricular end-diastolic volume. That extra filling stretches the cardiac muscle fibers more, increasing preload (and, through the Frank-Starling mechanism, can boost stroke work). Systemic vascular resistance affects afterload, not the filling of the ventricle, so it doesn’t directly raise preload. End-systolic volume reflects what remains after contraction and is influenced by contractility and afterload, not by the filling phase.