Non-invasive Ventilation and High-speed Oxygen Therapy Effects on Heart Function - HiFlow-Heart Study

Inclusion Criteria: 1. Major patient 2. Patient who has undergone cardiac surgery with extracorporeal circulation for more than 24 hours and has been extubated for at least 6 hours. 3. Pre-operative heart failure with left ventricular ejection fraction \< 40%. 4. Invasive monitoring by pulmonary arterial catheter (Swan-Ganz) with transpulmonary thermodilution and by radial arterial catheter intended for use in the intra- and post-operative monitoring of the patient. 5. Treatment with conventional oxygen therapy (O2C) without an increase in O2 flow for more than 30 minuts, without signs of hypoxemia (SpO292%) 6. Stable hemodynamic parameters: no changes in hemodynamic parameters (arterial pressures and pulmonary and cardiac index) by more than 10% over the 30 minutes prior to inclusion and no increase in cardiotropic medication for at least 30 minutes. 7. Patient with an oxygenation rate ≤ 6L 8. For women of child-bearing age: negative pregnancy test at inclusion 9. Person who has read and understood the information letter and signed the consent form 10. Affiliation to a social security scheme Exclusion Criteria: 1. Contraindication to the use of NIV or HFO 2. Patient with orotracheal intubation or tracheotomy 3. Renal failure with hemodialysis or hemofiltration 4. Uncontrolled state of shock (PAS\<90 mmHg and/or cardiac index\<1.8 L/min/m² and/or norepinephrine\>0.2 μg/kg/min and/or dobutamine\>10 μg/kg/min) 5. Acute respiratory failure as defined by : * clinical signs: respiratory rate \>35/min, signs of struggle, SpO2\<92% on O2C * indication for treatment with NIV or HFO at the discretion of the clinician * oxygen dependency requiring O2C\>6L/min O2C flow at the oxygen mask 6. Chronic advanced respiratory disease 7. Chronic treatment with NIV or CPAP at home 8. Non-operated aortic or mitral insufficiency ≥ II/IV 9. Administration of loop diuretics within 3 hours prior to inclusion for intravenous forms and within 6 hours for oral forms. 10. Presence of altered consciousness defined by a Glasgow score \< 15/15 or cognitive dysfunction defined by a CAM-ICU score \> 0/4 11. Pregnant or parturient or nursing woman or proven lack of effective contraception 12. Person deprived of liberty by an administrative or judicial decision or person placed under judicial protection / subtutorship or guardianship 13. Person participating in another trial / having participated in another trial that may interfere with the procedures that are the subject of the research within a 4-week time frame