Aim: The effect of nitroglycerin on proper arterial stiffness of the arterial tree has not been fully clarified. The cardio-ankle vascular index (CAVI), which is an application of the stiffness parameter β theory on the arterial tree from the origin of the aorta to the ankle, was developed recently. Furthermore, the stiffness of the aorta (heart-thigh β (htBeta)) and of the femoral-tibial arteries (thigh to ankle β (taBeta)) could be monitored by applying the same theory. The effects of nitroglycerin on CAVI, htBeta, and taBeta were studied comparing the values of healthy people and those of arteriosclerotic patients.Methods: The subjects were healthy people (CAVI ＜7.5, n=25) and arteriosclerotic patients (CAVI ＞9, n=25). Nitroglycerin (0.3 mg) was administrated sublingually, and various arterial stiffness indices were measured at one-minute intervals for a period of 20 minutes using Vasera VS-1500 (Fukuda Denshi, Tokyo).Results: After the administration of nitroglycerin in healthy people, CAVI decreased significantly after 5 min. from 6.76(6.32-7.27) to 5.50(4.70-6.21), P＜0.05, and recovered after 15 min. htBeta from 5.10(4.76-5.76) to 3.96(3.35-4.79), P＜0.05, and taBeta from 14.41(10.80-16.33) to 10.72 (9.19-13.01), P＜0.05 also decreased significantly. In arteriosclerotic patients, CAVI decreased after 5 min. from 10.47(9.67-11.29) to 9.71(8.74-10.57), P＜0.05 and recovered after 15 min. htBeta did not significantly change from 12.00(11.46-13.21) to 11.81(10.14-13.83), ns, but taBeta decreased significantly from 18.55(12.93-23.42) to 12.37(9.68-16.99), P＜0.05.Conclusion: These results indicate that a nitroglycerin-induced decrease of arterial stiffness is more prominent in muscular arteries than in elastic arteries, and this effect was preserved much more prominently in arteriosclerotic patients than in healthy people.