BACKGROUND: Alarming somatic symptoms, in particular, cardiovascular symptoms, are the characteristic feature of panic attacks. Increased cardiac mortality and morbidity have been found in these patients. Power spectral analysis of electrocardiogram R-R intervals is known to be a particularly successful tool in the detection of autonomic instabilities in various clinical disorders. Our study aimed to compare patients with panic disorder and healthy controls in heart rate variation (HRV) parameters (very-low-frequency [VLF], low-frequency [LF], and high-frequency [HF] band components of R-R interval) in baseline and during the response to the mental task. SUBJECTS AND METHODS: We assessed psychophysiological variables in 33 patients with panic disorder (10 men, 23 women; mean age 35.9+/-10.7 years) and 33 age- and gender-matched healthy controls (10 men, 23 women; mean age 35.8+/-12.1 years). Patients were treatment naive. Heart rate, blood pressure, muscle tension, and HRV in basal conditions and after the psychological task were assessed. Power spectrum was computed for VLF (0.003-0.04 Hz), LF (0.04-0.15 Hz), and HF (0.15-0.40 Hz) bands using fast Fourier transformation. RESULTS: In the baseline period, the VLF band was significantly lower in panic disorder group compared to controls (p<0.005). In the period of mental task, the LF/HF ratio was significantly higher in panic disorder patients compared to controls (p<0.05). No significant differences were found in the remaining parameters. There was a significant difference in DeltaHF and DeltaLF/HF ratio between patients and controls, with Delta increasing in patients and decreasing in controls. CONCLUSION: These findings revealed that patients suffering from panic disorder were characterized by relative sympathetic dominance (reactivity) in response to mental stress compared with healthy controls.