The Protium heptaphyllum species, also known as Almécega, produces an oily resin, used in folk medicine as an analgesic and anti-inflammatory agent, in healing, and as an expectorant, which is rich in pentacyclic triterpenes and essential oils. In this study, the essential oil obtained by hydrodistillation of Almécega's resin was analyzed by gas chromatography-triple quadrupole mass spectrometry and evaluated for chemical composition and vasorelaxant activity in rat superior mesenteric artery. The main constituents determined by gas chromatography-triple quadrupole mass spectrometry were limonene, p-cineole, and o-cymene. In intact rings precontracted with phenylephrine (Phe 1 μM), EOPh (3-750 μg/mL) induced relaxation, and the essential oil had a concentration-dependent vasorelaxant effect, without involvement of endothelial mediators.