Background-Heart failure is a highly prevalent disorder that continues to be associated with repeated hospitalizations, high morbidity, and high mortality. Sleep-related breathing disorders with repetitive episodes of asphyxia may adversely affect heart function. The main aims of this study were to determine the prevalence, consequences, and differences in various sleep-related breathing disorders in ambulatory male patients with stable heart failure.Methods and Results-This article reports the results of a prospective study of 81 of 92 eligible patients with heart failure and a left ventricular ejection fraction <45%. There were 40 patients without (hourly rate of apnea/hypopnea, 4+/-4; group 1) and 41 patients with (51% of all patients; hourly rate of apnea/hypopnea, 44+/-19, group 2) sleep apnea. Sleep disruption and arterial oxyhemoglobin desaturation were significantly more severe and the prevalence of atrial fibrillation (22% versus 5%) and ventricular arrhythmias were greater in group 2 than in group 1. Forty percent of all patients had central sleep apnea, and 11% had obstructive sleep apnea. The latter patients had significantly greater mean body weight (112+/-30 versus 75+/-16 kg) and prevalence of habitual snoring (78% versus 28%). However, the hourly rate of episodes of apnea and hypopnea (36+/-10 versus 47+/-21), episodes of arousal (20+/-14 versus 23+/-11), and desaturation (lowest saturation, 72+/-11% versus 78+/-12%) were similar in patients with these different types of apnea.Conclusions-Fifty-one percent of male patients with stable heart failure suffer from sleep-related breathing disorders: 40% from central and 11% from obstructive sleep apnea, Both obstructive and central types of sleep apnea result in sleep disruption and arterial oxyhemoglobin desaturation. Patients with sleep apnea have a high prevalence of atrial fibrillation and ventricular arrhythmias.