Which term explains the relationship between venous return and the strength of ventricular contraction?

• A. Starling's Law
• B. Ejection Fraction
• C. Cardiac Output
• D. Diastole phase

Answer: (A)

Starling's Law describes how the amount of blood returning to the heart influences how strongly the ventricles contract. When venous return increases, the ventricles fill more during diastole, raising the end-diastolic volume. This stretches the cardiac muscle fibers to a more optimal length, improving the overlap of actin and myosin, so the next contraction is stronger. The result is a higher stroke volume, helping the heart balance the outputs of the two ventricles.

Other terms describe different things. Ejection Fraction is about the percentage of the filled volume that is ejected, not the mechanism linking filling to contraction strength. Cardiac Output is the total amount pumped per minute (heart rate times stroke volume), not the specific relationship between venous return and contraction force. The diastole phase refers to the relaxation and filling period, not the contractile response to filling.