Limited information exists on the relations between heart rate variability, hypertension, lifestyle factors and renin-angiotensin-aldosterone system. A total of 191 newly diagnosed yet untreated hypertensive men and women, 35-54 years of age, were compared with an age- and gender-stratified random population sample of 105 normotensive men and women to find out independent determinants of heart rate variability. Heart rate variability was computed from 5-min ECG time series using the standard deviation of normal-to-normal RR intervals (SDNN), the square root of the mean of squared differences between adjacent normal RR intervals (RMSSD) and the fast Fourier transform spectral analysis. All absolute measures of heart rate variability were reduced in hypertension (P<0.001 for each, ANOVA). In multivariate regression analyses, reduced heart rate variability was independently associated with higher heart rate (P<0.001 for all absolute measures of heart rate variability), higher age (P=0.001 for SDNN, total and LF powers; P<0.001 for RMSSD and HF power) and higher mean arterial pressure (P<0.05 for total power, P<0.01 for the other absolute measures) but not with sodium and alcohol intakes, body mass index and smoking. Increased plasma renin activity (PRA) was an independent attributor of reduced HF power (P<0.05) and reduced RMSSD (P<0.01). Increased blood pressure and heart rate are associated with decreased heart rate variability without any direct effects on heart rate variability of lifestyle factors. High PRA is an independent determinant of diminished modulation of vagal activity.