Doppler echocardiographic measurements of blood flow velocity and acceleration in the ascending aorta have been shown to be useful descriptors of left ventricular (LV) systolic function. Few data exist, however, regarding the influence of loading conditions, particularly afterload, on these Doppler measurements in human subjects. Therefore, 14 normal volunteers (mean age 28 years) were studied using continuous wave Doppler echocardiography performed from the suprasternal notch both at baseline and during a controlled infusion of methoxamine. LV peak systolic (delta pk) and end-systolic (delta ES) wall stresses were calculated noninvasively using blood pressure and echocardiographic dimensions. Heart rate was kept constant by transesophageal atrial pacing. Methoxamine resulted in significant increases in mean systolic (163 +/- 8 vs 129 +/- 10 mm Hg) and diastolic (93 +/- 7 vs 71 +/- 12 mm Hg) blood pressure, as well as delta pk (277 +/- 25 vs 222 +/- 40 g/cm2 x 10(3] and delta ES (97 +/- 26 vs 77 +/- 19 g/cm2 x 10(3] (p less than or equal to 0.0004 for all). Conversely, peak velocity decreased from 0.91 +/- 0.18 m/s at baseline to 0.8 +/- 0.18 m/s (p less than or equal to 0.002) and peak acceleration decreased from 22 +/- 5 m/s2 at baseline to 19 +/- 5 m/s2 (p less than or equal to 0.006) during methoxamine infusion. Flow velocity integral and LV end-diastolic dimension remained unchanged. Thus, aortic flow velocity and peak acceleration are inversely related to afterload. This relation should be considered when using serial determinations of these Doppler parameters for patients in whom changing levels of afterload might occur.