Which of the following mechanisms is a positive contributor to stroke volume?

Increased preload is a fundamental mechanism that positively contributes to stroke volume. Preload refers to the initial stretching of the cardiac muscle fibers prior to contraction, which is largely influenced by the volume of blood returning to the heart (venous return). When preload increases, it enhances the stretching of the ventricles, following the Frank-Starling principle, which states that within physiological limits, the greater the stretch of the cardiac muscle fibers, the more forcefully they will contract. This increased force of contraction results in a more significant volume of blood being ejected from the heart during systole, thus increasing stroke volume.

When the heart fills with more blood during diastole (increased preload), it is able to pump out more blood during each contraction, elevating overall stroke volume. This is vital for maintaining adequate cardiac output and is especially important during periods of increased physiological demand, such as exercise.