If venous return increases (and preload increases) assuming contractility is constant, what happens to stroke volume?

If venous return increases (and preload increases) assuming contractility is constant, what happens to stroke volume?

• A. Stroke volume decreases
• B. Stroke volume increases
• C. Stroke volume remains unchanged
• D. Stroke volume becomes unpredictable

Answer: (B)

The main idea is the Frank-Starling relationship: increasing venous return raises end-diastolic volume (preload), and with contractility held constant, the heart responds by contracting more forcefully. This stronger contraction ejects more blood during systole, so the stroke volume increases. In other words, more filling leads to a greater amount of blood pumped out per beat when the muscle’s intrinsic ability to contract isn’t changing. The increase in stroke volume assumes afterload and contractility stay the same, and it won’t rise indefinitely if the muscle is stretched beyond its optimal length.

The main idea is the Frank-Starling relationship: increasing venous return raises end-diastolic volume (preload), and with contractility held constant, the heart responds by contracting more forcefully. This stronger contraction ejects more blood during systole, so the stroke volume increases. In other words, more filling leads to a greater amount of blood pumped out per beat when the muscle’s intrinsic ability to contract isn’t changing. The increase in stroke volume assumes afterload and contractility stay the same, and it won’t rise indefinitely if the muscle is stretched beyond its optimal length.