•Congestion in acute heart failure affects survival curves and length of stay.•Our comparisons revealed that the higher the hydration status, the longer the LOS.•BIVA measurements are independent predictor of length of stay in acute HF patients. Congestion in acute heart failure (AHF) affects survival curves and hospital length of stay (LOS). The evaluation of congestion, however, is not totally objective. The aim of this study was to verify the accuracy of bioelectrical impedance vector analysis (BIVA) in predicting the LOS in AHF patients. This is a retrospective study. A total of 706 patients (367 male; mean age: 78 ± 10 y) who had been admitted to hospital with an AHF event were enrolled. All underwent anthropometric and clinical evaluation, baseline transthoracic echocardiography, and biochemical and BIVA evaluations. The comparison among the clinical characteristics of congestion, LOS, and hyperhydration status revealed that the higher the hydration status, the longer the LOS (from 7.36 d interquartile range: 7.34–7.39 d in normohydrated patients to 9.04 d interquartile range: 8.85– 9.19 d in severe hyperhydrated patients; P < 0.05). At univariate analysis, brain natriuretic peptide, blood urea nitrogen, New York Heart Association class, hemoglobin, hydration index, and peripheral edema all had a statistically significant influence on LOS. At multivariate analysis, only brain natriuretic peptide (P < 0.0001), blood urea nitrogen (P = 0.011), and hydration index (P < 0.0001) were significantly associated to LOS. Congestion evaluated by BIVA is an independent predictor of length of total hospital stay in HF patients with acute decompensation. The quick and reliable detection of congestion permits the administration of target therapy for AHF, thus reducing LOS and treatment costs.