What is Frank Starling's Law of the Heart?

What is Frank Starling's Law of the Heart?

• A. Stroke volume is independent of venous return.
• B. Stroke volume increases in response to an increase in the end-diastolic volume.
• C. Heart rate always decreases with increased preload.
• D. Contractility is unaffected by preload.

Answer: (B)

Frank-Starling's law describes how the heart adjusts its pumping strength based on how much it is filled. When venous return increases, the end-diastolic volume (the preload) rises, so the ventricular muscle fibers are stretched closer to their optimal length. This stretch enables a stronger contraction, leading to a greater stroke volume. In other words, stroke volume rises as end-diastolic volume increases, up to a point, matching the amount of blood returning to the heart and helping balance output between the two sides. This isn’t about heart rate or about preload having no effect on contractility. Heart rate is influenced by autonomic factors and other mechanisms, not fixed to preload. And while contractility is an intrinsic property of the myocardium, the core idea here is how preload (through end-diastolic volume) directly increases the force of contraction and thus stroke volume.

Frank-Starling's law describes how the heart adjusts its pumping strength based on how much it is filled. When venous return increases, the end-diastolic volume (the preload) rises, so the ventricular muscle fibers are stretched closer to their optimal length. This stretch enables a stronger contraction, leading to a greater stroke volume. In other words, stroke volume rises as end-diastolic volume increases, up to a point, matching the amount of blood returning to the heart and helping balance output between the two sides.

This isn’t about heart rate or about preload having no effect on contractility. Heart rate is influenced by autonomic factors and other mechanisms, not fixed to preload. And while contractility is an intrinsic property of the myocardium, the core idea here is how preload (through end-diastolic volume) directly increases the force of contraction and thus stroke volume.