BACKGROUND: Among patients with heart failure, sleep-disordered breathing is a common problem, with a prevalence ranging from 24% to 76%. Encompassed within the general category of sleep-disordered breathing are 2 types of sleep apnea: obstructive sleep apnea (OSA) occurs when the oropharyngeal musculature relaxes, causing a collapse of the upper airway, and central sleep apnea occurs when the brain stem fails to stimulate breathing. METHODS AND RESULTS: This article focuses on the relationship between heart failure and OSA, the treatment of OSA with continuous positive airway pressure (CPAP), and the role of CPAP in improving such effects of heart failure as ejection fraction, blood pressure, sympathetic activity, sleepiness, heart rate, and mortality. CONCLUSIONS: It is important to distinguish the type of sleep-disordered breathing a patient may have. Further studies are needed to elucidate the effects of CPAP and other therapies.