Which statement describes the Frank-Starling law?

Which statement describes the Frank-Starling law?

• A. Heart rate increases with increased preload
• B. Cardiac output is independent of venous return
• C. Preload only affects afterload
• D. Stroke volume increases in response to increased preload (venous return) due to greater stretch of myocardial fibers

Answer: (D)

The main idea being tested is how stretching the heart before it contracts affects how much blood it can pump. This stretch, preload, comes from venous return filling the ventricles during diastole. When more blood returns, the ventricles fill more, the myocardial fibers are stretched to a greater length, and the heart can generate a stronger contraction because the length-tension relationship in cardiac muscle is optimized at that stretched length. The result is a higher stroke volume, allowing the heart to eject more blood in response to the greater preload, helping match output to the amount of blood returning. This isn’t about heart rate changing with preload, and it isn’t about afterload limiting contraction. It’s specifically about how increased preload leads to a stronger contraction and greater stroke volume. So the statement that stroke volume increases in response to increased preload (venous return) due to greater stretch of myocardial fibers best captures what the Frank-Starling law describes.

The main idea being tested is how stretching the heart before it contracts affects how much blood it can pump. This stretch, preload, comes from venous return filling the ventricles during diastole. When more blood returns, the ventricles fill more, the myocardial fibers are stretched to a greater length, and the heart can generate a stronger contraction because the length-tension relationship in cardiac muscle is optimized at that stretched length. The result is a higher stroke volume, allowing the heart to eject more blood in response to the greater preload, helping match output to the amount of blood returning.

This isn’t about heart rate changing with preload, and it isn’t about afterload limiting contraction. It’s specifically about how increased preload leads to a stronger contraction and greater stroke volume. So the statement that stroke volume increases in response to increased preload (venous return) due to greater stretch of myocardial fibers best captures what the Frank-Starling law describes.