Preload refers to which concept?

• A. Stroke Volume
• B. Preload
• C. Afterload
• D. Cardiac Output

Answer: (B)

Preload is the amount of stretch on the ventricular muscle fibers at the end of filling, right before contraction. This stretch comes from how much blood returns to the heart and fills the ventricle during diastole, and is closely approximated by the end-diastolic volume or pressure. The bigger the preload (within normal limits), the stronger the next contraction tends to be due to the Frank-Starling mechanism, which helps determine stroke volume. This concept is distinct from stroke volume (the actual amount ejected per beat), afterload (the pressure the ventricle must overcome to eject blood), and cardiac output (the total volume pumped per minute). So preload specifically describes the filling state of the ventricle just before it contracts.