What is the effect of stimulating the vagus nerve on the heart rate?

Stimulating the vagus nerve has a well-documented effect on heart rate, primarily leading to a decrease in heart rate. The vagus nerve is part of the parasympathetic nervous system, which is responsible for promoting a "rest and digest" state in the body. When the vagus nerve is stimulated, it releases neurotransmitters that bind to receptors in the heart, specifically leading to a reduction in the rate of electrical impulses generated by the sinoatrial (SA) node, which is the natural pacemaker of the heart.

This vagal stimulation slows down the heart rate by increasing the activity of acetylcholine in the heart, counteracting the effects of the sympathetic nervous system, which tends to elevate heart rate and cardiac output. As a result, the overall effect of vagal stimulation is bradycardia, or a decreased heart rate, making the correct choice in this scenario clearly aligned with known physiological responses.