Observer variability may limit assessment of aortic stenosis by Doppler echocardiography. This study aimed to assess whether echocardiographic contrast agent improves reproducibility of aortic valve area (AVA) measurements for patients with aortic stenosis. In all, 20 patients with aortic stenosis (67 +/- 10 years old) underwent noncontrast and contrast Doppler echocardiography on 2 occasions, 3 weeks apart. Intraobserver and interobserver coefficients of reproducibility were 0.36 and 0.20 cm for left ventricular outflow tract (LVOT) diameter, and 0.38 and 0.24 cm(2) for AVA, respectively. Although intraobserver reproducibility was unaffected, contrast improved interobserver reproducibility for LVOT diameter (mean of differences -0.02 +/- 0.07 cm vs 0.01 +/- 0.10 cm, P <.05) and AVA (mean of differences 0.02 +/- 0.10 cm(2) vs 0.07 +/- 0.12 cm(2), P <.05). Prevalve and postvalve velocities were increased with contrast compared with noncontrast imaging (prevalve, 1.07 +/- 0.20 vs 0.94 +/- 0.19 m/s, P <.01; postvalve, 3.76 +/- 0.87 vs 3.47 +/- 0.78 m/s, P <.01). We conclude that contrast significantly increases Doppler velocities and produces modest improvements in reproducibility of LVOT diameter and AVA. We suggest that, when assessing patients with aortic stenosis, contrast agents should be considered in patients who are difficult to image with poor baseline LVOT images or Doppler studies, or where there is poor interobserver reproducibility.