This study investigated the effect of sildenafil on uterine volumetric flow (UVF) and vascular impedance in nonpregnant, nulliparous women. Fifteen women were randomized in a double-blind fashion to receive either placebo, or sildenafil (25 or 100 mg) during the luteal phase of the menstrual cycle. Color Doppler ultrasound of both uterine arteries was performed at baseline and 1 and 3-hours post-dosing to calculate resistance index (RI) and UVF. Those who received sildenafil significantly increased UVF and decreased RI over the three hour monitoring period. When UVF responses to sildenafil were examined as a function of baseline UVF, a significant increase in UVF was observed in only those subjects with higher baseline UVF. Overall, women in the luteal phase demonstrated a significant increase in UVF in response to sildenafil. However, this increase appears to be directly associated with basal UVF.