Obstructive sleep apnea (OSA) is present in more than 50% of patients referred to cardiac rehabilitation units. However, it has been under-recognized in patients after stroke and heart failure. Those with concurrent OSA have a worse clinical course. Early treatment of coexisting OSA with continuous positive airway pressure (CPAP) results in improved rehabilitation outcomes and quality of life. Possible mechanisms by which CPAP may improve recovery include decreased blood pressure fluctuations associated with apneas, and improved left ventricular function, cerebral blood flow, and oxygenation. Early screening and treatment of OSA should be integral components of patients entering cardiac rehabilitation units.