To determine the associations of age, blood pressure (BP) and cardiac structure with left ventricular (LV) diastolic performance, 47 subjects (21 normotensives and 26 age-matched, previously untreated hypertensives) were studied by 24-hour ambulatory BP monitoring, radionuclide ventriculography and sector-guided M-mode echocardiography. Normotension was defined as an awake ambulatory BP less than 130/80 mm Hg and hypertension as an awake ambulatory BP greater than 135/85 mm Hg. Univariate analyses revealed strong negative correlations of LV filling rate with age (r = -0.67, p less than 0.001), 24-hour systolic or diastolic BP (r = -0.59 for systolic BP and -0.57 for diastolic BP, p less than 0.001 for both) and a modest positive correlation with LV ejection fraction (r = 0.42, p less than 0.05). After multivariate analysis, significant dependencies of both the left atrial index and LV mass index on ambulatory BP were found, which negated the significance of the relation of these 2 cardiac structural variables with LV filling rate. The final regression equation predicted LV filling rate from age, BP and LV ejection fraction. Age was the most important single correlate of LV filling, as evidenced by the 14 of 16 subjects (88%) over the age of 53 years (8 hypertensives, 6 normotensives) who had reduced LV filling rates compared with only 9 of the remaining 31 subjects (29%, all hypertensives) under the age of 53 years with reduced LV filling rates. These data demonstrate that LV filling rate is more dependent upon age and BP than left atrial or LV size.(ABSTRACT TRUNCATED AT 250 WORDS)