Abstract: In a constant pressure perfused swine coronary artery preparation, Danshensu, β(3,4-dihydroxyphenyl) lactic acid a constituent from S. miltiorrhiza Bge was found to dilate the coronary artery and antagonize significantly the constricting responses elicited by doses of morphine and propranolol. These interactions might be of practical importance when either propranol or morphine is administered concomitantly with Danshensu in treating severe angina episodes. In this experiment, the morphine-induced coronary constriction seemed to bear no relation to histamine or opiate receptors, since it was neither antagonized by the antihistamine agent (Antazoline) nor by naloxone. Although the propranolol induced coronary constriction was speculated partly due to the alpha adrenoreceptor dominance accompanying beta-blockade, the mechanism of antagonism by Danshensu remains to be investigated. In addition, Danshensu showed no antagonistic effect on the contracture response of coronary artery elicited by high potassium medium.