Final answer:
Decreased contractility will cause a decrease in stroke volume because it leads to weaker heart muscle contractions and smaller volumes of blood being ejected during systole.
Step-by-step explanation:
The factor that will cause a decrease in stroke volume (SV) is D) Decreased contractility. Contractility refers to the force of the contraction of the heart muscle, and is a primary parameter impacting the volume of blood ejected from the ventricles during systole (SV). When the heart contracts with less force, it results in a smaller SV and a larger end-systolic volume (ESV). Negative inotropic factors, which decrease contractility, lead to less forceful contractions and consequently reduce SV.