REN and pulmonary arterial hypertension: First, hyponatremia is known to be related to higher mortality in patients with diseases activating the renin-angiotensin system and increasing vasopressin secretion, such as heart failure [8, 9], liver cirrhosis [10, 11], pulmonary embolism [12], pulmonary hypertension [13, 14], pneumonia [15, 16], and myocardial infarction [19, 20].