The cardiovascular effects of dehydroevodiamine, an alkaloid isolated from Evodia rutaecarpa Jussieu, were studied in both in vivo and in vitro experiments. The in vivo experiments revealed that i.v. administration of dehydroevodiamine elicited a slight but significant reduction in blood pressure and a marked decrease in heart rate which was confirmed by an increased cycle length of the electrocardiogram. However, a hemodynamic experiment with microspheres showed that the total peripheral resistance was not altered by dehydroevodiamine. The blood flows of various organs were not significantly changed except those of kidney and skin, in which blood flow was decreased. In vitro, the spontaneously beating atria were significantly suppressed by dehydroevodiamine in a dose-dependent manner. These findings suggested an important effect of dehydroevodiamine in suppressing the heart, which may largely contribute to the hypotensive effect of this alkaloid. However, its vasodilator effect on hindquarter muscles cannot be neglected.