Load changes were obtained in 7 females with untreated primary hypertension by means of controlled intravenous infusion of sodium nitroprusside (0.2 mg/ml), in order to assess variations in the more usual indexes of left ventricular (LV) contractility to different loads and to verify that those indexes were independent of load. 2D-controlled M-mode echocardiograms were performed at baseline and when systolic blood pressure (SBP) had been reduced by 7, 16 and 23% for at least 5 min. Heart rate did not change during the test; decrease in SBP was associated with either decreases in both end-systolic dimension (LVIDs) and end-systolic stress (ESS), or an increase in systolic function. SBP/LVIDs, SBP/end-systolic volume (ESV) and ESS/LVIDs ratios were examined and compared as indexes of contractile state. SBP/ESV and ESS/LVIDs ratios showed great variation at all stages as compared to baseline values, while the SBP/LVIDs ratio did not change. The percent variation between the baseline values and the last stage of the test was 51% for the ESS/LVIDs ratio, 37% for the SBP/ESV and 5% for the SBP/LVIDs ratio. Best-fitting regression showed that a linear relationship existed only between SBP and LVIDs. Echocardiographic two-dimensional (as ESS) or three-dimensional derivations (as ESV) should be carefully employed when the contractile state is studied, while the SBP/LVIDs ratio can be easily used as a baseline value, as it is insensitive to changes in load.