Sympathetic stimulation causes the veins and arteries to constrict, which in turn affects how fast the heart beats, according to Medscape. It also affects heart contraction and relaxation.
Exercising, emotional distress, dehydration and losing blood cause the sympathetic nervous system to stimulate the heart indirectly via blood vessels. This can increase the heart rate, make it contract harder and cause faster relaxation. As the blood vessels narrow, the heart has to respond by meeting new physical demands.
Patients who undergo unusual sympathetic activation of the heart may experience chest pain. Such chest pain can indicate angina, or it may be a symptom of heart disease.