To determine whether alterations of left ventricular (LV) structure are associated with improved LV function under chronic clonidine monotherapy (300-450 g/day) of essential hypertension, 11 male patients (age range 47-61 years) were followed for 5.4 +/- 0.9 months using echocardiography and Doppler echocardiography. Blood pressure decreased from a mean of 168/105 to 150/96 mmHg (p < 0.01), heart rate remained unchanged (73 +/- 10 vs. 71 +/- 10 beats/min). LV muscle mass decreased from 350 +/- 73 to 297 +/- 56 g (p < 0.02), LV volume/muscle mass ratio increased from 0.58 +/- 0.13 to 0.69 +/- 0.12 ml/g (p < 0.005). Ejection time increased from 276 +/- 17 to 296 +/- 17 ms (p < 0.01), whereas no significant change was found for pre-ejection period, ejection fraction, cardiac index and LV dimensions. Doppler analysis revealed improved isovolumic relaxation time (116 +/- 17 vs. 84 +/- 28 ms; p < 0.05), but no change in isovolumic contraction duration, maximal inflow velocities, time-velocity integrals and their duration, rate of acceleration and deceleration of early and atrial filling, and of their ratios. It is concluded that no reliable improvement in diastolic or systolic LV function is observed in chronic clonidine monotherapy of essential hypertension despite a normalization of blood pressure and a regression of LV hypertrophy.