To evaluate the role of losartan on left ventricular (LV) function of hypertensive patients. Hypertensive patients (n=19) underwent evaluation of systolic and diastolic LV function, using radionuclide ventriculography (RVG), before and at 3mo into the treatment with the angiotensin II antagonist losartan. All patients underwent a baseline 12 lead ECG and an echocardiogram (ECHO), which was also repeated at 3mo into treatment. Results are expressed as mean±SEM and statistics were performed using paired t-test. A p value ≤0.05 was considered significant. Treatment with losartan for 3mo had no effect on LV mass measured by echo (141±5 vs. 139±6g/m2). The LV ejection fraction, measured by RVG, was unchanged by treatment when compared to the baseline study (58±2% vs. 57±2%, respectivelly, p=0.49). Considering all patients involved in the study (n=19), the LV "Peak Filling Rate" (PFR), a parameter of diastolic function measured by RVG, was also unchanged by treatment when compared to baseline (2.5±0.2EDV/s vs. 2.5±0.3EDV/s, respectively, p=0.9). However the analysis of those patients with evidence of diastolic dysfunction (n=12) on the baseline RVG (PFR<2.5EVD/s), demonstrated significant improvement of LV filling after therapy with losartan (PFR =1.8±0.1EDV/s vs. 2.3 ±0.2EDV/s, respectively, p=0.05). This change was associated with improvement of symptoms. Our results demonstrated that hypertensive patients with diastolic dysfunction on radionuclide ventriculography have significant improvement of ventricular filling at 3mo into treatment with losartan. (Hypertens Res 1999; 22: 155-159)