Final answer:
The direct answer to the question is B. increases the venous return, as sympathetic stimulation of the heart enhances cardiac contractility and heart rate by releasing neurotransmitters such as norepinephrine, thereby increasing venous return.
Step-by-step explanation:
Sympathetic stimulation of the heart increases heart rate and contractility, which is described as a positive inotropic effect. Parasympathetic stimulation, on the other hand, has a negative inotropic effect, often involving the neurotransmitter acetylcholine (ACh), which tends to slow the heart rate by increasing the permeability of SA nodal cells' membrane to potassium, thus extending repolarization. Therefore, sympathetic stimulation is associated with the release of norepinephrine (NE) that speeds up heart rate and contractility, while ACh released during parasympathetic stimulation slows down heart rate.
The correct answer to the question is B. increases the venous return, because sympathetic stimulation causes vasoconstriction which increases venous return to the heart, thereby enhancing cardiac output. This effect is mediated by neurotransmitters like NE and epinephrine that act on the heart's beta receptors to increase metabolic rate and the force of contraction, ultimately leaving a smaller residual end-systolic volume (ESV) in the ventricles.