This thesis follows and assembles what I did during a six-months traineeship at Actelion Janssen. Once the company's therapeutic areas of interest are briefly described, the emphasis in this work is on one of them: Pulmonary Hypertension (PH). Then, a WHO classification and available diagnostic tests for this disease are examined and two clinical studies in PH labelled TRACE and CIPHER are outlined: the first is a multicenter, double-blind, placebo-controlled, phase 4 study to evaluate the effect of Uptravi treatment on the daily life physical activity of patients with pulmonary arterial hypertension, while the second one is a prospective, multicenter study designed to identify a biomarker signature for the early detection of PH and another signature to distinguish two sub-classes of this pathology from the others.