Vagal tone is the activity of the vagus nerve, the 10th cranial nerve, and a fundamental component of the parasympathetic branch of the autonomic nervous system. This branch of the nervous system is not under conscious control and is largely responsible for the regulation of several body compartments at rest. Vagal activity results in various effects, including heart rate reduction, vasodilation/constriction of vessels, glandular activity in the heart, lungs, digestive tract, liver, immune system regulation as well as control of gastrointestinal sensitivity, motility, and inflammation.