Which statement best describes the Frank-Starling mechanism?

• A. An increase in preload will have no effect on the next contraction.
• B. An increase in preload will increase the next ventricular contraction.
• C. An increase in afterload will increase stroke volume.
• D. Preload changes do not affect myocardial oxygen demand.

Answer: (B)

The main concept tested is how the stretch of cardiac muscle fibers at the end of filling ( preload ) affects the strength of the next heartbeat. When venous return increases, the ventricle fills more, raising the end-diastolic volume. This stretches the myocardial fibers to a longer length, which brings actin and myosin into a more favorable overlap for cross-bridge formation. As a result, the force of the next contraction increases, producing a stronger beat and a larger stroke volume. This intrinsic length–tension relationship is the Frank-Starling mechanism, helping the heart automatically match its output to the amount of blood returning to it.

So, increasing preload makes the next contraction stronger, rather than having no effect. And while afterload and other factors influence stroke volume too, the key idea here is that preload-induced stretch boosts the force of the subsequent contraction.