An increased preload is equivalent to, or causes, a(n) _______.

An increased preload is equivalent to, or causes, a(n) _______.

• A. Increased EDV
• B. Decreased EDV
• C. Increased heart rate
• D. Decreased contractility

Answer: (A)

Preload is the initial stretch of the ventricular myocardium just before it contracts, driven by venous return. That stretch corresponds to the end-diastolic volume inside the ventricle. So when preload increases, the ventricle fills more, raising the end-diastolic volume. This is exactly why an increased preload is equivalent to an increased EDV. This relationship is the basis of the Frank-Starling mechanism: more EDV stretches the muscle to a more favorable length, increasing the force of contraction (and thus stroke volume) up to a limit. Preload itself doesn’t directly dictate heart rate or contractility, which is why those options don’t fit.

Preload is the initial stretch of the ventricular myocardium just before it contracts, driven by venous return. That stretch corresponds to the end-diastolic volume inside the ventricle. So when preload increases, the ventricle fills more, raising the end-diastolic volume. This is exactly why an increased preload is equivalent to an increased EDV. This relationship is the basis of the Frank-Starling mechanism: more EDV stretches the muscle to a more favorable length, increasing the force of contraction (and thus stroke volume) up to a limit. Preload itself doesn’t directly dictate heart rate or contractility, which is why those options don’t fit.