Diplotropis ferruginea Benth. (Fabaceae) is a tree popularly known in Northeastern Brazil as “sucupira-preta”. In the present work, the isolation, identification and pharmacological activity of a furanoflavan-type flavonoid (2,3-trans-3,4-trans)-3,4,5,8-tetramethoxy-(6,7,2”,3”)-furanoflavan, which received the trivial name diplotropin is reported. The structure was determined by means of spectroscopic techniques, especially EIMS and 1D and 2D NMR. Diplotropin (10⁻⁸ −3 · 10⁻⁴ M) inhibited the phasic contractions induced by both acetylcholine (IC₅₀ = 4.6±0.8 · 10⁻⁵ M) and histamine (IC₅₀ = 2.3±1.1 · 10⁻⁵ M) in guinea-pig ileum. Diplotropin relaxed the ileum pre-contracted with KCl (EC₅₀ = 3.9±1.1 · 10⁻⁶ M), acetylcholine (EC₅₀ = 3.7±1.6 · 10⁻⁶ M) and histamine (EC₅₀ = 4.4±1.4 · 10⁻⁵ M) in a concentration-dependent manner. As the maintenance of tonic contraction induced by these contractile agents involves Ca²⁺ influx through voltage-dependent Ca²⁺ channels, it is suggestive that this relaxation may be due to the blockade of Ca²⁺ influx through those channels. This hypothesis was confirmed by the observation that diplotropin antagonized (pD’₂ = 4.83±0.37) CaCl₂ induced contractions in Ca²⁺-free depolarizing medium (IC₅₀ = 1.5±0.8 · 10⁻⁵ M).