Stroke volume increases with all of the following EXCEPT ____________.

Stroke volume, which is the amount of blood ejected from the heart with each contraction, is influenced by several factors, including preload, contractility, and afterload.

An increase in preload refers to the volume of blood filling the heart, which stretches the ventricular walls and enhances contraction strength due to the Frank-Starling mechanism. This typically leads to an increase in stroke volume.

Contractility is the intrinsic ability of the heart muscle to contract. When contractility increases, the heart can pump more effectively, resulting in an increased stroke volume.

Conversely, afterload is the resistance the heart must overcome to eject blood during systole. An increase in afterload makes it more difficult for the heart to pump blood, which can lead to a reduction in stroke volume. If the heart is faced with higher resistance (afterload), it cannot eject as much blood with each contraction, thus decreasing stroke volume.

This distinction helps clarify why an increase in afterload does not contribute to an increase in stroke volume, making it the correct answer in this context.