Low heart rate variability (HRV) level, indicative of impaired autonomic function, is associated with an increased risk of cardiovascular morbidity and mortality and is negatively affected by hypercholesterolaemia. In order to test the hypothesis that significant low density lipoprotein (LDL) cholesterol reduction after treatment with a statin will have a beneficial effect on HRV level in hypercholesterolaemic patients with or without coronary artery disease (CAD), forty consecutive patients (28 men and 12 women) with a median age of 61, range (17--70) years were studied. Twenty had stable CAD and 20 were free of CAD at baseline. Twenty healthy volunteers, of similar age and gender as the patients, were used as controls. Patients were treated with atorvastatin (20 mg/day) for 2 years. Changes in lipid parameters and HRV indices were assessed at baseline and 2 years later in all subjects. In both patient subgroups a significant beneficial change in all lipid parameters (more pronounced in the CAD+ subgroup) and a significant beneficial modification in HRV time and frequency domain indices was recorded (more pronounced in the CAD- subgroup), while lipid parameters and HRV indices remained unchanged in the control group. A correlation between LDL concentrations and most of the HRV indices was found at baseline in both patient subgroups, while no such correlation was found between values or their percent changes after hypolipidaemic treatment. These data suggest that treatment with atorvastatin improves autonomic function, as reflected by an increase in HRV level, and this may be a likely mechanism, at least in part, for the reduction in clinical events reported by the landmark survival studies with statins in primary and secondary CAD prevention. Perhaps, if this finding is confirmed by larger studies, HRV level may prove to be a useful tool for risk-stratification and treatment guide in high-risk patients with hypercholesterolaemia, regardless of CAD.