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Summary Introduction Chronic heart failure and sleep apnea are common diseases. The sleep apnea syndrome occurs as a central or an obstructive form. The central sleep apnea is caused by a failure in respiratory control whereas the reason for the obstructive form is an upper airway collaps. Different methods can be used to diagnose sleep apnea syndrome. The polysomnography (PSG) is the gold standard. It examines breathing parameters and involves an electroencephalogram (EEG). This allows an in depth sleep stage analysis. The polygraphy (PG) is easier to apply since a reduced number of parameters is used (for example no EEG is registered). In this study PG and PSG were compared to examine whether the PG detected and characterised the sleep associated breathing disorders for patients with pre-existing chronic heart failure as correct as the gold standard PSG. Materials and methods This study used data from the SAHERZ register of the „Schlafmedizinisches Zentrum“, at the universiy of Marburg (269 patients with an ejection fraction (EF) < 50 %). The database allowed a comparison between both methods, the PSG and the PG. To obtain these data, sleep parameters for every patient from a single night was used. One analysis was done using data from all available PSG channels, a second analysis consisted of measurements from only those channels which are usually available for PG measurements. Results The mean age oft the 269 patients was 60.1 ± 13.9 years. 75.8 % were male, 83.2 % showed NYHA class 2 or higher. The mean EF was 33.7 ± 10.3 %. The mean number of respiratory events per night was 133 for the PG method and 95 for the PSG method. In majority these were central respiratory events. The patients were assigned to AHI category I to IV on the basis of their individual frequency of respiratory events. About one third of the patients exhibited AHI category I (no sleep apnoe - PG: 82 of 267: 30.7 %; PSG: 75 of 267: 28.0 %). PG classified 78.3 % of the patients in the same AHI category as PSG. The degree of severity was underestimated in 17.9 % by PG and overestimated in 3.7 %. There was no significant correlation between personal (age, sex, BMI) or sleep related parameters and the deviation between PG and PSG classification of AHI. Discussion The diagnosis of an existing sleep apnea syndrome should be as exact and reliable as possible in order to provide the best therapy for a patient with chronic heart failure. In this study the PG diagnosis underestimated the AHI in many patients. These patients are in danger of not getting adequate therapy. As a consequence PG should be used only in specific situation for diagnosis of sleep apnea syndrome in chronic heart failure patients.