The vagus nerve affects heart rate by increasing blood vessel dilation and lowering blood pressure, according to Healthline. Vagus nerve stimulation can cause a drop in blood flow to the brain and a loss of consciousness known as vasovagal syncope.
The vagus nerve is a part of the body’s parasympathetic system; it slows the heart rate and helps return the body to a state of calm after a stressful or threatening experience. It is also responsible for setting a person’s resting heart rate, explains the Sarver Heart Center. Higher vagus nerve activity can accompany lower resting heart rates.
The vagus nerve extends from the brain stem to the atria of the heart, notes Circulation, an American Heart Association medical journal. At the heart, the vagus nerve releases the neurotransmitter acetylcholine onto the sinus node that controls the pace of the heartbeat. This produces relaxation and stimulates the dilation of blood vessels, counteracting the heightened awareness caused by the sympathetic system and allowing the heart rate to slow.
Strong vagus nerve activity is responsible for the slow heart rates of many athletes, reports the Sarver Heart Center. However, an abnormally slow heart rate can indicate a heart defect in non-athletes and is a predictor of mortality, according to Circulation.