Noninvasive ventilation (NIV) as an adjunct strategy for increasing exercise tolerance has been widely investigated in patients with pulmonary diseases. To our knowledge, there are no studies that have used NIV during exercise in patients with decompensated heart failure (HF). The aim of this study was to evaluate the effects of NIV on exercise tolerance in hospitalized patients with decompensated HF. Thirteen patients (77 ± 15 years) with a mean left ventricular ejection fraction of 35 ± 15% were included. Patients underwent 2 submaximal exercise tests with constant load for lower limbs using a portable cycle ergometer. Tests were performed on the same day with a 60-minute interval between each one, using a randomized crossover design: sham ventilation (continuous positive airway pressure mode, 4 cm H₂O) and intervention situation (NIV in bilevel mode). Primary outcome was the endurance time performed during exercise tests with constant load. Submaximal exercise with NIV in bilevel mode improved endurance time (7.2 ± 2.7 minutes) compared to the tests performed with continuous positive airway pressure (5.1 ± 1.5 minutes; p = 0.008). Increase in endurance time (Δ time) with bilevel test showed a significant correlation with reduction in the slope of dyspnea (Δ Borg) over time (r = −0.73; p = 0.004). There was a significant correlation between endurance time in bilevel tests and maximum inspiratory pressure % predicted (r = 0.68; p = 0.02). In conclusion, NIV was effective in increasing exercise tolerance in hospitalized patients with decompensated HF. (ClinicalTrials.gov registration NCT02122848).