OBJECTIVE To determine whether patients with congestive heart failure who develop Cheyne-Stokes respiration (CSR) during sleep experience excessive daytime sleepiness. This was addressed by comparing sleep quality and daytime sleepiness in three groups: patients with CHF and CSR during sleep (CSR group), patients with CHF without CSR (CHF group), and healthy control subjects (control group). METHODS Single-blind, cross-sectional study. METHODS Patients referred by cardiologists and control subjects recruited from the general community. METHODS Twenty-three men: 7 in the CSR group, 7 in the CHF group, and 9 in the control group. METHODS Each subject had an overnight sleep study and an assessment of sleepiness the following day. RESULTS The three groups were a similar age: CSR, 68 +/- 5 years; CHF, 62 +/- 4 years; and control, 65 +/- 4 years; and left ventricular ejection fraction was the same in patients with CSR (20 +/- 1.5%) and CHF (23 +/- 5%). Sleep latency was significantly shorter in patients with CSR (4 +/- 1.1 min) than patients with CHF (11.3 +/- 4.8 min) and healthy controls (12.4 +/- 1.9 min) and was within the diagnostic range of severe sleepiness. Patients with CSR had significantly more stage 1 and 2 non-rapid eye movement (NREM) sleep (CSR, 83 +/- 7; CHF, 64 +/- 9; control, 63 +/- 9% total sleep time), less REM sleep (CSR, 10 +/- 3; CHF, 22 +/- 8; control, 22 +/- 7% total sleep time), and a higher frequency of arousals from sleep (CSR, 30 +/- 16; CHF, 18 +/- 15; control, 10 +/- 2/h of sleep); 66% of arousals were associated with CSR. Regression analysis revealed that sleep latency was inversely related to the amount of stage 1 and 2 NREM sleep (r = -0.67), arousal frequency (r = -0.46), and the apnea-hypopnea index (r = -0.63) and was positively correlated with the amount of slow-wave sleep (r = 0.45) and REM sleep (r = 0.56) and the mean oxygen saturation during sleep (r = 0.50). CONCLUSIONS Patients with CHF who develop CSR experience excessive daytime sleepiness due to sleep disruption. This should be considered the clinical evaluation of these patients' daytime complaints.