Between June 2015 and December 2017, 180 patients with chronic heart failure caused by rheumatic heart disease, cardiomyopathy and coronary heart disease (in Cardiology Department and Cardiothoracic Surgery Department of the First Affiliated Hospital of Nanjing Medical University), were screened for sleep apnea by polysomnography (PSG). Of them, 20 obstructive sleep apnea (OSA) and 20 central sleep apnea (CSA) were enrolled. Clinical evaluations including NYHA class, electrocardiographic, echocardiographic, arterial blood gas analysis findings, baseline medication, and 6-minute walk test (6MWT) were recorded.