Final answer:
Parasympathetic nervous system stimulation on the heart results in a decreased heart rate and decreased force of contractions.
Step-by-step explanation:
The effects of parasympathetic nervous system stimulation on the heart are a decreased heart rate and decreased force of contractions. Parasympathetic stimulation releases acetylcholine (ACh) at the neuromuscular junction, which hyperpolarizes and inhibits contraction to decrease the strength of contraction and stroke volume. This stimulation primarily affects the upper chambers (atria) of the heart, reducing the atrial kick and leading to a decrease in ventricular stretch and preload.