Inclusion Criteria:  age over or equal 18 years old admitted in an Emergency Department acute respiratory failure defined by a respiratory rate over or equal 25 breathes/min or signs of increased work of breathing clinical suspicion of acute heart failure defined bu the European Cardiologic Society.  Exclusion Criteria:  patient requiring immediate invasive mechanical ventilation neurologic distress defined by a Glasgow Coma Scale under 13 haemodynamic failure defined by a Mean Blood Pressure under 65 mmHg or patient requiring catecholamines