Stability of indexes of heart rate variability (HRV) has not been established for patients with congestive heart failure (CHF). We therefore measured Holter-derived HRV indexes in 17 stable patients with class II or III CHF (mean age 52 +/- 9 yr; 5 men and 12 women) on two occasions 2 weeks apart. Stability was determined via paired t tests and intraclass correlation coefficients (ICCs). ICCs for time domain indexes of HRV were > or = 0.86 for 24 hours, > or = 0.73 for daytime, and > or = 0.72 for nighttime indexes reflecting longer-term variability. After log transformation, ICCs for the short-term 24-hour measures PNN50 (percentage of N-N intervals > 50 msec different from preceding interval) and RMSSD (the root mean square of successive differences) were 0.85 and 0.67. ICCs for frequency domain indexes of HRV were 0.86 to 0.91. We compared HRV indexes, serum norepinephrine (NE) levels, and respiratory sinus arrhythmia induced by paced breathing, also considered measures of autonomic tone. NE correlated weakly with average R-R interval, and all indexes of HRV reflecting longer-term variation (r = -0.32 to r = -0.50). ICC was 0.78 for NE. Respiratory sinus arrhythmia was highly repeatable (ICC = 0.70) but did not correlate significantly with NE or any measure of HRV. We conclude that time and frequency domain indexes of HRV are stable over time in CHF patients without intervening events.