Polygonum viviparum (PV) promoted an increase in nitric oxide (NO) production by human umbilical vein endothelial cells (HUVECs). Cells were treated with 3, 10, 30, and 100 μg/ml PV for 1 h. Medium was then collected for NO detection using the Griess reagent. Data are expressed as the mean ± standard error of the mean (S.E.M.) for more than 5 individual determinations. Treatment with acetylcholine (ACh) was used as a positive control. * p < 0.05, ** p < 0.01, significantly different from the control.