Which statement best describes the Frank-Starling mechanism?

• A. Increasing end-diastolic length increases stroke volume
• B. Higher afterload increases stroke volume
• C. Increased contractility increases end-diastolic volume
• D. Starling's law relates heart rate to oxygen consumption

Answer: (A)

The Frank-Starling mechanism shows how the heart adjusts its pumping strength based on how much the ventricles are stretched at the end of filling. When end-diastolic length increases, the cardiac fibers are stretched more, moving toward an optimal overlap of actin and myosin, which strengthens contraction and increases stroke volume. This is why a rise in ventricular filling (preload) leads to a higher stroke volume within the heart’s normal operating range. So, the statement that increasing end-diastolic length increases stroke volume best captures this relationship.

Higher afterload tends to reduce stroke volume unless contractility rises to compensate, and increased contractility can boost stroke volume without necessarily increasing end-diastolic length. Starling’s law describes the relationship between end-diastolic volume and stroke volume, not heart rate or oxygen consumption.