Which of the following best defines preload?

• A. Preload is the rate of venous return.
• B. Preload is the peak LV pressure during systole.
• C. Preload is the time delay between atrial and ventricular contraction.
• D. Preload is LV wall stretch at end-diastole, tightly linked to end-diastolic volume.

Answer: (D)

Preload is the initial stretch of the left ventricle at the start of contraction, set by how much blood fills the ventricle during diastole. This stretch corresponds to end-diastolic volume (and the end-diastolic pressure) and determines how forcefully the heart can contract via the Frank‑Starling mechanism. That’s why the best definition is the left ventricular wall stretch at end-diastole, tightly linked to end-diastolic volume.

The other ideas mix in related concepts but aren’t the definition of preload: the rate of venous return influences how much fills the ventricle but preload itself is about the stretch from filling; peak LV pressure during systole reflects contractile strength and afterload more than filling; and a time delay between atrial and ventricular contraction describes conduction timing, not filling stretch.