It is a common but unsubstantiated belief that blood flows through the left ventricular outflow tract (LVOT) with a spatially uniform velocity. Doppler echocardiography was performed to study in an apically obtained view of the LVOT the profile of subaortic velocities in 79 subjects free of clinical heart disease. The systolic velocities and time intervals were determined in the medial and lateral margins and the center of the LVOT. Peak systolic velocity measured 98 +/- 16 cm/s (mean +/- SD) in the medial margin of the LVOT close to the subaortic ventricular septum, 89 +/- 14 cm/s in the midline of the LVOT, and 79 +/- 14 cm/s in the lateral margin of the LVOT close to the base of the mitral valve (p < 0.001). The respective means of the velocity-time integrals were 19 +/- 3, 17 +/- 3 and 14 +/- 3 cm (p < 0.001). Systolic time intervals determined from the flow signals differed also statistically significantly across the recording sites in the LVOT. The velocity measurements obtained in the center of the LVOT were nearly identical with the values averaged over all measurements across the LVOT. It is concluded that the systolic flow velocity profile in the LVOT is not flat, as has been assumed, but skewed toward faster flow along the subaortic ventricular septum. Measurements made in the center of the LVOT can be used as surrogate for the spatial average velocities.