Pulmonary Arterial Hypertension (PAH) includes a heterogeneous group of clinical entities sharing similar clinical and pathological features that have been subcategorized as idiopathic PAH (IPAH, formerly known as "primary pulmonary hypertension" or PPH), familial PAH, pulmonary hypertension related to connective tissue diseases (such as systemic sclerosis), portopulmonary hypertension and pulmonary hypertension related to HIV infection, drugs and toxins (10). PAH is clinically defined by a resting mean pulmonary artery pressure ≥ 25 mmHg and pulmonary artery wedge pressure ≤ 15 mmHg in the absence of left heart disease, underlying parenchymal lung disease, thromboembolic disease or other causes of pulmonary hypertension.