Patients with congestive heart failure (CHF) frequently demonstrate Cheyne-Stokes respiration (CSR) with repetitive arousals and oxygen desaturations during sleep. Although it was evident from early publications that CSR during the daytime is a poor prognostic indicator in patients with CHF, it was speculated recently that CSR occurring during sleep could impede left ventricular function and even survival. We therefore followed up 36 patients with CHF and a left ventricular ejection fraction < or = 40% who underwent a sleep study at our institution. The patients showed a reduced ejection fraction (20 +/- 8%) and CSR with a median of 19% of total sleep time (lower and upper quartiles 9% and 56%). In 12 +/- 9% of their time in bed, the arterial oxygen saturation was <90%. No patient was lost to follow-up, which lasted for 32 +/- 15 months (range 11 to 53). One-year survival was 86 +/- 6%, and 2-year survival was 66 +/- 8%. Univariate comparisons for survival between groups stratified by the amount of CSR revealed no significant difference (log rank test, p = 0.84). However, the 20 patients with a left ventricular ejection fraction <20% had a shorter mean survival time than patients with an ejection fraction >20% (9.5 vs 28.3 months; log rank test, p = 0.013). Two patients with CSR during the daytime died within 1 month. No other patient had CSR during the daytime, and only 1 patient without daytime CSR died within 1 month (chi-square test, p <0.001). Higher age, reduced carbon dioxide end-tidal partial pressure, and increased transit time were found to be significantly related to the amount of nocturnal CSR. In conclusion, CSR occurring during sleep has no important prognostic impact in patients with CHF, but CSR present during the daytime suggests a high likelihood of dying within a few months.