the cardiovascular effects of vasicine, an alkaloid isolated from the leaves of sida cordifolia l., were evaluated in this work. in non-anaesthetized rats (n=6), vasicine (1, 2.5, 5 and 10 mg/kg; i.v., randomly) induced hypotension associated with an intense bradycardia. both responses were completely abolished after atropine (2mg/kg; i.v.) and attenuated after hexamethonium (20 mg/kg; i.v.). in isolated rat mesenteric artery rings, vasicine (0.03, 0.1, 0.3, 1, 3, 10, 30, 100 and 300 μg/ml, cumulatively) induced concentration-dependent relaxation of phenylephrine-induced tone (ic50= 3.8±0.9 μg/ml; n = 6). in conclusion, the results show that vasicine produce hypotension and bradycardia which appears to be due to the stimulation of cardiac muscarinic receptors (directly and/or indirectly), and by a decrease of the peripheral resistances.