OBJECTIVE: In chronic heart failure (CHF) episodes of decompensation may be linked to derangements within cardiovascular reflex control. We investigated changes in autonomic tone in patients with decompensated CHF. METHODS: We examined 17 patients with decompensated CHF (14 men, age 62 +/- 2 years, LVEF 32 +/- 3%) on admission and after clinical stabilization. Control group consisted of 9 patients (8 men, age 64 +/- 7 years, LVEF 30 +/- 7%) with stable CHF. Assessment of autonomic tone was based on 5-min ECG and blood pressure recordings using time and frequency domains of heart rate variability (HRV) and a sequence method to derive baroreflex sensitivity (BRS). RESULTS: On admission, decompensated CHF patients had reduced HRV indices (p < 0.05) and depressed BRS (p < 0.01) as compared to those with stable CHF. After clinical stabilization (4 +/- 2 days of treatment) time domain HRV indices and BRS increased (SDNN, 34.4 +/- 5.4 vs. 55.8 +/- 9.8 ms; RMSSD, 38.4 +/- 12.0 vs. 51.1 +/- 10.4 ms; BRS, 4.3 +/- 0.7 vs. 7.6 +/- 1.3 ms/mmHg; all p < 0.01) and became similar to those seen in stable CHF patients. Breathing with oxygen affected autonomic indices neither in decompensated nor in stable CHF patients. Eight patients developed an episode of additional CHF worsening during hospitalization, in whom the third assessment was performed on discharge. Worsening in clinical status was followed by a decrease in HRV and BRS that became similar to those noted on admission. INTERPRETATION: HRV measures and BRS are severely deranged in the acute phase of CHF decompensation. Clinical stabilization results in an improvement of autonomic indices. However, subsequent clinical worsening adversely affects HRV and BRS.