Little is known about optimal level of positive end-expiratory pressure (PEEP) in patiens who recieved invasive mechanical ventilation for acute decompensated heart failure. We therefore sought to compare clinical outcome according to low versus high PEEP.

Inclusion Criteria:

1. Subject who was diagnosed with congestive heart failure and objective evidence of pulmonary congestion (pulmonary edema on simple chest radiography or positive B-line on lung ultrasonography AND elevated B-type natriuretic peptide or N-terminal pro-brain natriuretic peptide level) as a reason for invasive mechanical ventilation
2. Age over 19 years old
3. Subject who agrees to the study protocol and the schedule of clinical follow-up, and provides informed, written consent, as approved by the appropriate Institutional Review Board/Ethical Committee of the clinical site.

Exclusion Criteria:

1. Subject who are on mechanical circulatory support (ECMO, intra-aortic balloon pump, VAD) at the time of randomization
2. Subject who has cardiac abnormality that requires emergent or urgent percutaneous or surgical valvular procedure
3. Subject who are on vasoactive or inotropic agents at least moderate dose defined as vasoactive-inotropic score >10
4. Isolated preload-dependent cardiac dysfunction (isolated right ventricular failure, right ventricular infarction, constrictive pericarditis, cardiac tamponade, severe pulmonary hypertension without LV dysfunction)
5. Predominant right ventricular failure defined as following; clinical evidence of right ventricular failure by attending physician's discretion including hepatojugular reflux, Kussmaul sign, cardiac liver cirrhosis, hepato/splenomegaly, acites, thronmbocytopenia, etc.
6. Subject who are not on mechanical ventilation before open heart surgery
7. Subject who received unwitness cardiopulmonary rescucitation (CPR) or witness CPR lasting more than 30 minutes
8. Subject who was already diagnosed or is suspected to have hypertophic cardiomyopathy with significant left ventricular outflow tract (LVOT) obstruction
9. Subject with intracranial hemorrahge or ischemic stroke at the time of randomization
10. Subject with irreversible neurologic damage or irreversible hepatic failure
11. Invasive mechanical ventilation lasting more than 24 hours preceding endotracheal intubation
12. Subject with underlying chronic obstructive pulmonary disease (GOLD classification III or IV) or restrictive pulmonary disease (e.g. interstitial lung disease)
13. Subject with impaired consciousness that can not perform self coughing and need suction to maintain adequate airway patency
14. Pregnant and/or lactating women
15. Subject with life expectancy less than a year
16. Subject who is not suitable to enrollment by investigator's discretion