In the last decade, the use of non-invasive respiratory support, such as high-flow nasal oxygen has become widespread in the setting of the Cardiology Intensive Care Unit. The possibility of high gas flow with high O2 concentrations is a good tool for critically ill patients, above all regarding its reduced side effects and better compliance. The physiological effects of this therapy and its impact on the management of airway and oxygen support in the complex picture of heart failure are objects of this chapter.