What primarily determines ventricular preload?

• A. End-diastolic volume
• B. End-systolic volume
• C. Heart rate
• D. Systemic vascular resistance

Answer: (A)

Preload is the stretch of the ventricular myocardium at the end of filling, so it’s determined mainly by how much blood is in the ventricle when diastole ends. That filling amount is the end-diastolic volume. When venous return is high or filling time is longer, EDV increases, stretching the ventricular fibers more and producing a stronger contraction via the Frank-Starling mechanism. End-diastolic volume is essentially the measure of preload because it directly reflects the volume available to stretch the ventricle before it contracts. End-systolic volume, on the other hand, is the amount left after contraction and doesn’t determine preload. Heart rate can alter filling time and thus influence preload indirectly, but it’s not the primary determinant. Systemic vascular resistance affects afterload, not preload.