The Frank-Starling mechanism describes the relationship between venous return and which cardiac parameter?

• A. Heart rate
• B. Stroke volume
• C. Blood pressure
• D. Cardiac output remains the same

Answer: (D)

The key idea is how the heart’s pumping strength adjusts to how much blood returns to it. When more blood returns to the heart, the ventricles fill to a higher end-diastolic volume. This stretches the cardiac muscle fibers so they can contract more forcefully. The stronger contraction ejects more blood with each beat, so stroke volume increases. Since cardiac output equals stroke volume times heart rate, stroke volume changing with venous return means CO will rise if heart rate stays the same. So the Frank-Starling mechanism describes the link between venous return and stroke volume, not heart rate, blood pressure, or a constant CO.