Saururus chinensis has been widely used as a traditional medicine for the treatment of beriberi, hypertension, pneumonia, edema, jaundice and gonorrhea. However, there is only limited information on the cardiovascular effects of S. chinensis extract or its single compounds. The present study was performed to investigate the effects of active lignans isolated from the extract of S. chinensis on vascular responses and heart functions. The vasorelaxant activity-guided fractionation of roots extract of S. chinensis led to the isolation of eight lignans as active principles. These lignans produced concentration-dependent relaxations of the endothelium-intact aortic preparations of rat aorta. Particularly, saucerneol ( 1), saucerneol D ( 2) and machilin D ( 8) exhibited distinctive vasorelaxant activity (EC (50) values: 2.2, 12.7 and 17.8 microM, respectively), which were significantly inhibited by removal of functional endothelium or pretreatment with N(G)-nitro-L-arginine methyl ester. Saucerneol ( 1) and saucerneol D ( 2) caused a significant decrease in left ventricular pressure, +dP/dt (max) and heart rate in isolated hearts. These results suggest that several lignans including saucerneol ( 1), saucerneol D ( 2) and machilin D ( 8), isolated from the ethanol extract of the roots of S. chinensis, have significant cardiovascular effects such as vasorelaxant and negative inotropic actions.