Introduction: Dyspnea and fatigue are the main clinical symptoms of heart failure and primarily responsible for exercise intolerance found in this syndrome. Now, It is known that the use of NIV in CPAP mode applied before exercise increases exercise tolerance in people with heart failure; however, it's not yet known if the bi-level mode is able to generate similar or even better results, due to pressure increase of the ventilatory support in this modality. Moreover, it is possible that there is influence between the pressure levels set in the NIV and the magnitude of its effect on the exercise in this population Objective: 1) test for differences between the acute effects of NIV on exercise tolerance in patients with HF, when applied CPAP or bi-level mode; and 2) check for discrepancies in the acute effects of Bi-level mode on the physical performance of these individuals, when applied at different pressure levels. Methodology: This is a controlled, randomized, double-blind and cross-over clinical trial, to be composed of 45 volunteers of both genders, aged between 30 and 80 years, with chronic heart failure, functional class II and III (New York Heart Association) in clinical stability. The experiment will be carried out on four different days, with a 48-hour interval between them, in which NIV will be used in the following modes: Bi-level with minimum parameters (EPAP = 6 cmH2O and IPAP = 12 cmH2O), Bi-level with maximum parameters EPAP = 8 cmH2O and IPAP = 14 cmH2O) and CPAP (6 cmH2O). Thus, all the volunteers will participate in the four TGC. During the tests, distance walking, perceived levels of fatigue and dyspnea, affective response, as well as other physiological variables will be analyzed. Statistical analysis, the ANOVA test for repeated measurements will be used, followed by the Bonferroni post-test, considering p-value less than or equal to 0.05 as statistically significant. Expected Results: This work is expected to improve the therapeutic management of HF patients, assisting in the implementation and improvement of methods to improve dyspnea and muscle fatigue, thus increasing tolerance to exercise.

This study is a randomized controlled trial, double-blind and cross-over, to be composed of 45 volunteers of both genders, aged between 30 and 80 years, with CHF will be selected from a specialized outpatient clinic with medical consent. Patients should have symptoms of compensated CHF; presenting functional capacity II and III (New York Heart Association), with left ventricular ejection fraction <50%; not participating in cardiac rehabilitation programs; and clinical stability in the last three months, with no history of angina or coexistence of obstructive pulmonary disease (Tiffeneau-Pinelli index> 70% in spirometry). In addition, they should not present any osteoarticular or neurological disease would prevents them from performing the proposed tests, as well as having a score higher than 22 in the Leganés cognitive test (20). In the case of NIV or exercise intolerance, as well as in case of non-attendance to the experiments on the scheduled days, subjects will be excluded from the study.

The sample will be the result of a non-probabilistic sampling process, calculated based on the magnitude of the effect of the main variable (distance traveled) after the use of NIV therapy, obtained in a pilot study. In addition, this protocol was aproved by the institution's Ethics Committee on Human Research (CAAE: 49324415.0.000.5537).

Experimental procedure The experimental protocol will occur in three visits, one per day, with a minimum interval of 48 hours between them. On the first visit, the volunteers will undergo a screening that consists of clinical evaluation (assessment sheet) and cognitive (Leganéscognitive test), as well as evaluation of lung function (spirometry) and QoL (Minnesota Living with Heart Failure Questionnaire). Next, the Shuttlel Walking Test (SWT) control (T-Co) will be performed, without previous use of NIV, in order to determine the distance traveled and other physiological variables in the absence of interventions. Finally, during the initial visit, a preliminary NIV session will be held to adjust the interface and adapt the volunteer to the therapy.

At each subsequent visit, volunteers will perform a SWT immediately after 30 minutes of NIV, one day in Bi-level mode and one in CPAP mode, following a randomized sequence. Thus, all volunteers will perform one SWT after CPAP (T-CP) and one SWT after Bi-level (T-Bi). In the experiment, the CPAP pressure will be maintained at 6 cmH2O, while at the Bi-level an expiratory pressure (EPAP) of 6 cmH2O and an inspiratory pressure (IPAP) of 12 cmH2O will be defined.

Inclusion Criteria:

1. Outpatient and have a compensated HF, without hospitalizations in the last three months;
2. Present functional class II and III (New York Heart Association);
3. Present left ventricular ejection fraction (LVEF) ≤ 50%;
4. Have not suffered myocardial infarction in the last three months;
5. No previous diagnosis of chronic obstructive pulmonary disease (FEV1 / FVC ratio> 70% in spirometry);
6. Do not be a smoker;
7. Not being pregnant;
8. Does not present any clinical disease or restriction of osteomioarticular or neurological origin that prevents / limits the carrying out of the proposed tests;
9. Integral cognitive functions, which were evaluated by the cognitive test of Leganés - PCL

Exclusion Criteria:

1. Unstable angina or significant arrhythmias;
2. Acute atrial fibrillation or total atrioventricular block;
3. Systemic blood pressure (AP) at uncontrolled rest (≥ 180/110 mmHg or ≤80 / 40mmHg);
4. Resting heart rate (HR) ≤ 40 bpm or ≥ 120 bpm;
5. Need for dialysis;
6. Use of bronchodilator;
7. Respiratory rate (RF) at rest ≥ 35 rpm;
8. Frequent vomiting;
9. Intolerance to NIV;
10. infection or fever.