Cheyne-Stokes respiration is common in congestive heart failure patients and causes cyclical fluctuation of the RR interval. We studied the characteristics of apnea-related heart rate variability (apnea HRV) and the relation between apnea HRV and oxygen desaturation was examined. Ambulatory electrocardiograms and data on respiration (oronasal flow, tracheal sounds, abdominal wall movement and oxygen saturation) were simultaneously recorded by a multi-channel digital recorder for 16 congestive heart failure patients (10 men and 6 women; mean age, 68 +/- 13 years). HRV occurred as a result of cyclical apnea attacks between 0.005 and 0.03 Hz (apnea band). Apnea HRV was obtained as the power ratio of apnea HRV normalized by the very low frequency band (0.003-0.04 Hz). Apnea HRV increased with the number of apnea episodes and the oxygen desaturation index, but no relation between apnea HRV and either mean oxygen density or oxygen desaturation time was observed. We concluded that apnea HRV is a predictor of the number of apnea attacks or oxygen desaturation, but does not reflect the degree of oxygen desaturation in Cheyne-Stokes respiration.