The associations of age, blood pressure and cardiac structure with rapid left ventricular filling were assessed in 47 subjects (21 normotensives and 26 age-matched untreated hypertensives) by 24-h ambulatory blood pressure monitoring, sector-guided M-mode echocardiography and radionuclide ventriculography. Univariate analyses revealed strong negative correlations of the left ventricular filling rate with age, and 24-h systolic and diastolic blood pressure, and a moderate positive correlation with the left ventricular ejection fraction at rest. Multiple regression analysis was performed with these variables, left atrial size and left ventricular mass index. Left atrial size and the left ventricular mass index were dependent on 24-h blood pressure, indicating that these two cardiac structural variables were less important than left ventricular filling. Age was undoubtedly the most important correlate of left ventricular filling, since 88% of the subjects over 53 years of age had reduced left ventricular filling rates regardless of the blood pressure status. However, under the age of 53 years, only the hypertensives had reduced filling rates. Thus, our study shows that the left ventricular filling rate is more dependent on age and 24-h blood pressure than on the left ventricular mass index. Furthermore, in patients over 53 years of age, it is not possible to separate the effects of hypertension on the diastolic function of the heart from the physiological alterations associated with ageing.