Possible roles of smooth muscle contractions in the vascular dynamics were studied in the isolated rat large artery which has previously been shown to generate spontaneous rhythmic contractions depending upon the extracellular Ca²⁺. A cylindrical segment of the common carotid artery was superfused externally and perfused intraluminally by Tyrode solution, and the steady state intraluminal pressure (P)-volume (V) relationship of the vessel was obtained. The pressure buffering characteristic (Windkessel effect) of the vascular wall was evaluated by measuring the intraluminal pressure swing during application of external alternating pressure (semi-triangular pressure pulse, 0-120mmHg, 300cycle/min, "dynamic pressure load") to the intraluminal space. Effects on these vascular dynamics of inhibition of spontaneous smooth muscle contraction during superfusion of the preparation with nominally Ca²⁺-free Tyrode solution were investigated. Spontaneous rhythmic fluctuations of the intraluminal pressure (0.2-1.0mmHg, 2-25cycle/min), presumably due to contractions of vascular smooth muscles, were detected. The Ca²⁺-free solution abolished these spontaneous changes in the intraluminal pressure and reduced the baseline intraluminal pressure. The volume distensibility (ΔV/(V•ΔP)) of the preparation at higher intraluminal fluid volumes (or pressures, higher wall stretch) was increased by Ca²⁺-free solution. The magnitude of intraluminal pressure swing and the maximum rate of changes in the pressure during application of "dynamic pressure load" were decreased in Ca²⁺-free solution. The results suggest that the inhibition of spontaneous contractions of smooth muscle by Ca²⁺-free solution may increase the volume distensibility and pressure-buffering function of the large elastic artery.