Which of the following factors affects stroke volume?

Preload, after-load, and contractility are key determinants of stroke volume, which is the amount of blood ejected by the heart with each contraction.

Preload refers to the degree of stretch of the cardiac muscle fibers just before contraction, which is influenced by the volume of blood returning to the heart. Increased preload typically enhances stroke volume due to the Frank-Starling mechanism, where more stretch allows for a stronger contraction.

After-load is the resistance the heart must overcome to eject blood. Higher after-load can reduce stroke volume as the heart has to work harder to pump blood into the circulation.

Contractility relates to the intrinsic strength of the heart muscle's contraction, independent of preload and after-load. Increased contractility enhances stroke volume, allowing the heart to pump more efficiently under the same preload and after-load conditions.

Together, these factors—preload, after-load, and contractility—are pivotal in determining how much blood the heart is able to pump with each beat, thus directly impacting stroke volume.