Which statement best defines preload?

• A. Afterload
• B. End systolic pressure
• C. End diastolic volume
• D. Heart rate

Answer: (C)

Preload is the filling stretch of the ventricle just before it contracts. This stretch is set by how much blood is in the ventricle at the end of diastole, which is the end-diastolic volume. That volume determines the initial sarcomere length and thus the force the heart can produce on the next beat (the Frank-Starling relationship).

End-diastolic volume is the direct measure of this filling state, so it best defines preload. When venous return increases, EDV rises, preload increases, and stroke volume tends to rise accordingly.

The other options describe different concepts: afterload is the pressure the ventricle must overcome to eject blood; end systolic pressure is the pressure in the ventricle at the end of systole; heart rate is the rate of beating and does not define the filling stretch.