The aim of this study was to assess the effects of losartan potassium, an angiotensin II receptor antagonist, on systolic blood pressure; diastolic blood pressure; and left ventricular dimensions, functions, and mass index (LVMI) in patients with mild-to-moderate essential hypertension. Twenty patients aged 40 to 65 years with either uncontrolled or previously untreated hypertension and echocardiographically documented left ventricular hyptertrophy (LVH) defined by LVMI >130 g/m(2) for men and >110 g/m(2) for women mere included in the study. Blood pressure measurements were taken at a-week intervals. Blood samples were taken before treatment and after 3 months of treatment for determination of Lipid concentrations and other laboratory variables used to monitor safety, and two-dimensional M-mode and Doppler echocardiographic measurements were obtained. Losartan was associated with a statistically significant reduction of mean systolic blood pressure from 173 +/- 6 mm Hg to 135 +/- 10 mm Hg and diastolic blood pressure from 100 +/- 4 mm Hg to 82 +/- 7 mm Hg without a change in heart rate. Significant decreases were identified in interventricular septal and left ventricular posterior wall thicknesses (from 12.5 +/- 0.8 mm to 11.5 +/- 0.8 mm and 12.1 +/- 1.0 mm to 11.1 +/- 0.8 mm, respectively). LVMI decreased from 138.8 +/- 18.7 g/m(2) to 126.0 +/- 21.8 g/m(2) after 3 months of treatment. Left ventricular dimensions and ejection fraction did not change significantly compared with baseline values. The Doppler echocardiographic assessment of mitral E/A ratio, which is a marker of diastolic function, increased significantly from baseline. Except for a significant increase in mean serum lactate dehydrogenase activity, laboratory findings (including serum lipid concentrations) remained constant. No clinical adverse effects attributable to losartan were observed. Results of this study suggest that losartan is an effective, well-tolerated drug that reduces LVH, improves left ventricular diastolic functions, and controls systolic and diastolic blood pressures in patients with mild-to-moderate essential hypertension.