Decreased heart rate variability has been associated with chronic congestive heart failure (CHF). We evaluated the effect of physical training on heart rate variability in 20 patients with CHF (NYHA class II to III) randomized to training (n = 8) and control (n = 12) groups. The training group underwent 3 months of physical training, by exercising on a bicycle ergometer for 30 min three times a week at a load corresponding to 50 to 60% of their peak oxygen consumption. Heart rate variability was assessed from 20-h ambulatory ECG recordings in the frequency domain, determined by high (0.15 to 0.40 Hz), low (0.04 to 0.15 Hz) and very low frequency (0.008 to 0.04 Hz) components. The high frequency component increased by 22 to 55% in the training group during the day (p = 0.0001) but not at night. The increase was seen during both sedentary and active periods. The low frequency/high frequency ratio attenuated in the training group during the day (p = 0.05) whereas an increase was seen in the control group throughout the day (p = 0.0003). Training lengthened the exercise duration by 71% at a submaximal workload (p = 0.01) and tended to increase the peak oxygen consumption by 15% (p = 0.09). These remained unchanged in the control group. In conclusion, physical training, which improves exercise capacity, ameliorates the autonomic derangement in CHF by increasing the parasympathetically mediated component of heart rate variability. It may thus influence favourably the prognosis of the disease.
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