Heart rate and age are independent variables associated with the pattern of normal left ventricular filling. Since heart rate variability also varies with age, the relationship between these and left ventricular filling in normal subjects was assessed. In 31 subjects (age range 21 to 71 years), power spectral analysis of heart rate variability was determined from 24 h Holter tapes, and left ventricular filling was assessed by Doppler echocardiography. Relationships between heart rate variability and left ventricular filling were assessed by univariate and multivariate regression analyses. Total, low frequency and high frequency power each significantly correlated with the peak filling velocity with atrial systole (A) (r = -0.70, P < 0.0001; r = -0.69, P < 0.0001; r = -0.54, P < 0.01, respectively), but did not correlate with measures of early diastolic left ventricular filling. Although age and A were related (r = 0.46, P < 0.010), age was no longer a significant variable when measures of heart rate variability were included in the multivariate regression model for A. Thus, the variability in measures of early diastolic filling in normal subjects appears to be independent of measures of heart rate variability, whereas, A is significantly associated with these measures.