Final answer:
An increase in sympathetic stimulation of the heart would increase stroke volume by increasing contractility.
Step-by-step explanation:
An increase in sympathetic stimulation of the heart would increase stroke volume by increasing contractility. Contractility refers to the force of the contraction of the heart muscle, which controls stroke volume. When sympathetic stimulation increases, it triggers the release of epinephrine and norepinephrine, which enhance both cardiac output and vasoconstriction, leading to an increase in stroke volume.