Doppler ultrasound permits noninvasive monitoring of aortic blood velocity. This study in 15 normal volunteers was undertaken to define the normal behavior of aortic Doppler velocity during change of body position as well as during static and dynamic exercise. Aortic velocity was markedly lower in the upright standing position compared with the supine position with a reduction of peak velocity (peak V) by 31 ± 5% (p < 0.01) and of the velocity time integral (VTI) by 51 ± 4% (p < 0.01). During bicycle exercise in the sitting position peak V progressively increased with increasing workload to 194 ± 15% (p < 0.01) of the resting value. The VTI increased at the lowest workload by 47 ± 9% (p < 0.01) and then remained constant at higher workload. During isometric handgrip exercise in the supine position neither peak V nor VTI changed significantly. The results indicate that aortic Doppler velocity critically depends on the body position. The variation of VTI during changes of body position and during exercise are similar in magnitude to those of stroke volume in previous studies employing invasive methods.