Based on a screening program of medicinal plants for their possible calcium antagonistic mode of action, the most active lipophilic extract of Ammi visnaga fruits (DAB 10) was fractionated by CC and investigated pharmacologically at K+ (60 mM)-depolarized guinea-pig aortic strips. Visnadin, khellin, and visnagin were identified and determined as the effective principles in this testing model with the dihydropyranocoumarin visnadin being the most active. Further selectivity tests against norepinephrine (100 microM)-induced contractions evaluated a possible pharmacological differentiation between these compounds as the furanochromones khellin and visnagin inhibited both spasms to a similar extent while visnadin's activity was significantly higher against K(+)-spasms, suggesting an involvement of a calcium channel blocking mode of action for visnadin.