Pipratecol is substituted thienoimidazole. It is the H+/K(+)-ATPase inhibitor. In a high concentration of 10(-4) g/ml, pipratecol increased the amplitude of isolated guinea-pig atrial contractions while decreased the rate. But, in a low concentration of 10(-8) g/ml, the drug decrease the amplitude and increased the rate slightly. The effects of adrenaline and noradrenaline were suppressed by the preceding addition of pipratecol, while that of isoproterenol was scarcely. The effect of pipratecol on atrial contractions was hardly influenced by reserpine with which the animal had been pretreated 24 hours before the sacrifice of animal. The augmentative effect of nicotine on atrial contractions was slightly suppressed by the preceding addition of pipratecol. From these results, it was assumed that pipratecol has some affinity with the adrenergic receptor of atria. As a peripheral vasodilator it has been used in conjunction with raubasine in the treatment of cerebrovascular disorders. Pipratecol was used as antiulcerative agent also.