Dimethyl pyrazine ethylamine hydrochloride (DPEH) is a synthetic analogue that acts through the blockade of calcium channels. The effect of DPEH on vascular smooth muscles was examined in this study using the rat aorta, tail artery and portal vein in vitro. On the portal vein, DPEH had a direct contractile effect that was dependent on the presence of extracellular Ca2+. It produced a depolarization-dependent potentiation of both aortic and portal vein contraction and dose-dependently increased the influx of extracellular calcium ions into aortic smooth muscles. It is therefore concluded that DPEH induces vascular smooth muscle contractility by acting as a calcium agonist.