We contrasted,in normotensive and oral,not oral L-arginine hypertensive rats, the changes of blood pressure, vasodilation and myocardium.The rats after aorta coarctation had severe hypertension and myocardial hypertrophy. L-arginine administration two weeks did not prevent the development from hypertension but could decrease myocardial hypertrophy in rats with aorta coarctation (heart weight/body weight ratio 3.78±0.19 vs 4.11±0.22mg/g, P< 0.05 ).The vasodilation to acetylcholine attenuated in isolated thoracic aorta from hypertensive rats with not oral L-arginine. L-arginine (10-5~10-3mol/L) induced concentration-dependent relaxation of thoracic aorta rings taken from hypertensive rats after aorta coarctation, but no effects on isometic tension of thoracic aorta rings from normotensive or oral L-arginine hypertensive rats.These findings suggest that L-arginine may attenu ate myocardial hypertrophy and improve vasodilation on hypertensive rats.This effects did not depend on the change of blood pressure.