Soluble guanylate cyclase (sGC) is one of the chemicals involved in the pathways controlling vascular tone, which is impaired in patients with PAH. This causes constriction and thickening of the blood vessels wall in the lungs and increase of blood pressure in the lungs. This can lead to the very debilitating symptoms of PAH such as tiredness, shortness of breath on exertion, collapse and often the inability of the patient to perform their daily life activities.