BACKGROUND Left ventricular function changes in the postmenopausal state. However, there are conflicting reports about the effects of oestrogen on left ventricular diastolic function in postmenopausal women. OBJECTIVE To evaluate the acute and chronic effects of oestradiol in physiological doses on diastolic heart function in hypertensive postmenopausal women with left ventricular diastolic dysfunction. METHODS A prospective, randomised, double blind, placebo controlled study was used to evaluate the effects of oestradiol in 34 hypertensive women with left ventricular dysfunction. The acute effects of a single 1 mg oral dose of oestradiol or placebo were determined after 90 minutes. The chronic effects of 1 mg oestradiol orally/day or placebo were determined after 12 weeks. Diastolic functional indices (mitral flow and pulmonary venous flow) were assessed by Doppler echocardiography. RESULTS Though an appropriate serum concentration was achieved, no acute effect of oestradiol administration on left ventricular diastolic function was identified. After 12 weeks of treatment the following changes (mean (SD)) were identified in the oestradiol group: a decrease in isovolumic relaxation time from 127 (23) to 106 (16) ms (p < 0.001), and in the deceleration time of the mitral E wave from 260 (42) to 238 (20) ms (p < 0.05); and an increase in the E/A ratio from 0.8 (0.2) (basal) to 1.0 (0.2) after 12 weeks (p < 0.001). CONCLUSIONS Hypertensive postmenopausal women who had hormone replacement therapy over a period of 12 weeks had significant improvement in left ventricular diastolic function. No changes were identified following acute administration.