"Danshen" has been used for the treatment of various cardiovascular diseases in the People's Republic of China for many years. Two different forms of "Danshen" exist, with the roots of Salvia miltiorrhiza being the traditional form and the roots of Salvia przewalskii being a surrogate used in the western areas of mainland China. The most abundant lipophilic diterpene quinones present in S. miltiorrhiza and S. przewalskii roots, tanshinone IIA (1) and cryptotanshinone (2), inhibited contraction of the isolated porcine coronary artery to the thromboxane A(2) analogue, U46619. Przewaquinone A (3), a lipophilic diterpene quinone present only in S. przewalskii, induced a similar but greater inhibitory action on vascular contraction than 1 and 2. This effect of 3 was endothelium-independent and reversible. The present results suggest that 3 is more potent than 1 and 2 and may contribute to a great extent to the ability of S. przewalskii roots to inhibit vascular contractions.