Preload is best described as the stretch of the ventricles at which point?

Preload is best described as the stretch of the ventricles at which point?

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

Answer: (A)

Preload is the amount the ventricles are stretched at the end of filling, just before they contract. That stretch comes from how much blood has filled the ventricle during diastole, which is best described by the end-diastolic volume—the volume of blood in the ventricle at the end of diastole. More venous return increases this volume, lengthens the sarcomeres, and, through the Frank-Starling mechanism, leads to a stronger beat. End-diastolic pressure can reflect filling, but the actual stretch is determined by the volume, not the pressure. End-systolic volume is what remains after contraction, not preload, and heart rate is independent of this ventricular stretch.

Preload is the amount the ventricles are stretched at the end of filling, just before they contract. That stretch comes from how much blood has filled the ventricle during diastole, which is best described by the end-diastolic volume—the volume of blood in the ventricle at the end of diastole. More venous return increases this volume, lengthens the sarcomeres, and, through the Frank-Starling mechanism, leads to a stronger beat. End-diastolic pressure can reflect filling, but the actual stretch is determined by the volume, not the pressure. End-systolic volume is what remains after contraction, not preload, and heart rate is independent of this ventricular stretch.