Evidence has accumulated suggesting that essential hypertension begins early in life and is potentially preventable. One possible pathogenetic mechanism implicated is a sympathetic nervous system abnormality which is manifested by increased sympathetic drive to the heart. An elevated sympathetic nervous system tone and decreased vagal inhibition is responsible for the hyperkinetic circulation seen in a significant proportion of persons with borderline essential hypertension. Exaggerated blood pressure and heart rate responses to mental stressors have been documented in normotensive children of hypertensive parents. These changes appear to involve sympathetic over-responding to fight-flight stimuli.