What is preload?

• A. The heart rate at rest
• B. The amount of blood in the ventricles after contraction
• C. The degree of stretch of ventricular myocardium at end of diastole (venous return)
• D. The pressure in the aorta during systole

Answer: (C)

Preload is the initial stretch of the ventricular myocardium just before it contracts, determined by how much blood returns to the heart during diastole. In other words, venous return fills the ventricles to end-diastolic volume, and that filling stretches the muscle fibers to set the starting length for contraction. This length-tension relationship—Frank-Starling—means that greater preload usually yields a stronger stroke, up to physiological limits. It’s not about the heart rate at rest, nor about the amount of blood remaining after contraction (that’s end-systolic volume), and it’s not the pressure in the aorta during systole (that’s afterload).