We studied five patients with chronic stable congestive heart failure (CHF), all of whom demonstrated recurrent apneas in association with Cheyne-Stokes respiration (CSR) during sleep. All five patients had symptoms consistent with a sleep apnea syndrome. Nasal continuous positive airway pressure (NCPAP) was administered at 8 to 12.5 cm H2O to all patients during sleep. The number of apneas fell from (mean +/- SE) 60 +/- 12/h of sleep on the control night to 9 +/- 7/h of sleep (p less than 0.01) on the NCPAP night, whereas mean nocturnal SaO2 rose from 88 +/- 2% on the control night to 92 +/- 2% (p less than 0.025) while on NCPAP. This was associated with resolution of symptoms of sleep apnea. In addition, resting left ventricular ejection fraction (LVEF) as measured by radionuclide angiography (RNA) rose from 31 +/- 8% while off NCPAP to 38 +/- 10% (p less than 0.05) while on NCPAP. Furthermore, all five patients experienced marked improvement in symptoms of heart failure from functional classes III and IV (New York Heart Association Classification) prior to NCPAP therapy to class II after NCPAP therapy was instituted. We conclude that, in certain patients, CSR during sleep associated with chronic CHF constitutes a sleep apnea syndrome, which can be alleviated by NCPAP. In addition, NCPAP therapy may lead to a reduction in cardiac dyspnea and improvement in left ventricular function.