We determined the acute effects of the angiotension converting enzyme inhibitor captopril on the arterial mechanics in rats at different ages, based on the exponentially tapered T-tube model. Male Wistar-Kyoto rats aged 4 and 12 months were individually referred to as young (n = 8) and adult rats (n = 8) and wereanesthetized and thoractomized. The pulsatile aortic pressure andflow signals before and after the administration of captopril (20mg/kg, i.p.) were measured by a high-fidelity pressure sensor andan electromagnetic flow probe, respectively. In each age group,captopril showed little change in basal heart rate as well ascardiac output. However, captopril produced a drop of 15% in meanaortic pressure in young and a fall of 12% in adult rats. Inaddition, captopril reduced total peripheral resistance by 21% inyoung and by 23% in adult animals. As for the pulsatile nature ofthe arterial system, captopril had increased wave transit time ofthe lower body circulation of 10% in young and of 12% in adultrats. By contrast, captopril reduced wave reflection factor by22% in young and by 25% in adult animals. In conclusion, theconverting enzyme inhibitor captopril has a stiffness-decreasingeffect on Windkessel vessels and a dilated effect on resistancearterioles in either young or adult rats. No age dependence ofvascular response and reflex tachycardia to captopril has beenfound in rats between 4 and 12 months.