Inclusion Criteria:  Adult patient (age > 18 years) Hospitalized in the intensive care and post-operative care unit of the Amiens-Picardie University Hospital Patient with ARDS (defined by the Berlin criteria) requiring mechanical ventilation with a P/F ratio < 200 and requiring iNO Beneficiary of social security Signature of the consent to participate in the study by the patient or, if unconscious, his legal representative/next of kin  Exclusion Criteria:  Pregnant or breastfeeding woman Contraindications to TEE (major upper gastro-intestinal surgery, mediastinal radiotherapy, active esophagitis, esophageal varices) Contraindications to the placement of an esophageal probe (recent upper gastro-intestinal surgery, active ulcer, active esophagitis) Presence of atrial fibrillation on echocardiographic examinations Contraindications to the administration of iNO Patients with chronic treatment allowing pulmonary arterial vasodilatation by sildenafil.