Objectives. Evaluation of the characteristics of sleep apnea (SA) in patients hospitalized with acute heart failure, considering that undiagnosed SA could contribute to early rehospitalization. Methods. 56 consecutive patients (13 women, 43 men, mean age 63.12 years) with acute heart failure, in stable condition, underwent nocturnal polygraphy before hospital discharge. The type and severity of SA was determined. Besides descriptive statistics, correlations between the severity of SA and clinical and paraclinical characteristics were also analyzed (t-test, chi-square test, significancy at alpha < 0.05). Results. 12 (21.4%) subjects were free of SA (AHI - apnea-hipopnea index <5/h), 15 (26.7%) had mild SA (AHI=5-14/h), 17 (30.3%) had moderate SA (AHI 15-30/h), and 12 (21.4 %) had severe SA (AHI>30/h). The apnea was predominantly obstructive (32 cases vs. 12 with central SA). Comparing the patients with mild or no SA with those with severe SA, we did not find statistically significant correlations (p>0.05) between the severity of SA and the majority of main clinical and paraclinical characteristics - age, sex, BMI, cardiac substrates of heart failure, comorbidities. Paradoxically, arterial hypertension (p=0.028) and atrial fibrillation (p=0.041) were significantly more prevalent in the group with mild or no SA. Conclusions. Before discharge, in the majority of patients hospitalized with acute heart failure moderate and severe SA is present, and is not related to the majority of patient related factors. Finding of significant SA in this setting is important, because its therapy could play an important role in preventing readmissions and improving prognosis.