Abstract Objective: The aim of this study was to explore whether the dilatation of the left ventricle and the deterioration of the ventricular function change the velocity distribution in the aortic annulus. Methods: Twenty patients with primary dilated cardiomyopathy and 20 patients with ischemic cardiomyopathy were studied. Doppler color flow mapping was used to construct instantaneous cross-sectional flow velocity profiles, and pulsed Doppler echocardiography was used to sample velocities across the aortic annulus. Results: (1) The velocity distribution was skewed with the highest velocities along the anterior and septal parts of the aortic annulus. The skewness of the velocity distribution in the apical long axis view was more pronounced than that in the four-chamber view. (2) Pulsed Doppler flow spectra sampled from the anterior, middle and posterior parts along the diameter of the aortic annulus in the long axis view also showed a skewed velocity distribution. The highest time-velocity integral (11.4 ± 0.7 cm) which was sampled from the anterior part was higher than the average time-velocity integral of three sampling sites (9.4 ± 0.6 cm) by 21.5 ± 1.7%, range 5.2–43.8%. However, the time-velocity integral sampled from the middle part (9.4 ± 0.6 cm) was very close to the average time-velocity integral ( r = 0.99; P < 0.01; SEE = 0.6 cm). Conclusion: In patients with dilated left ventricle and reduced ejection fraction, the velocity distribution in the aortic annulus is also skewed. The pulsed Doppler sampling site will significantly affect the accuracy of cardiac output measurement in the diagnosis and follow-up of this patient category.