Pulmonary hypertension is a fatal disease of multiple etiologies that is estimated to affect over 100 million people worldwide. The disease is defined hemodynamically as a mean pulmonary artery pressure ≥ 25 mmHg at rest. Pulmonary hypertension is a type of high blood pressure that affects the arteries in your lungs and the right side of your heart. The pulmonary circulation is responsible for carrying deoxygenated blood from the heart to the lungs and returning oxygenated blood back to the heart for delivery to the systemic circulation. The pulmonary circulation has a central role in cardiopulmonary gas exchange and oxygen transport. In one sort of pulmonary hypertension, called Pulmonary Arterial Hypertension (PAH), blood vessels in your lungs are narrowed, congested or damaged. The damage slows blood flow through your lungs, and blood pressure in the lung arteries rises. Your heart must work harder to pump blood through your lungs. The extra effort eventually causes your heart muscle to develop weak and fail. There are three types of pulmonary arterial hypertension based on the origin of the cause: idiopathic, heritable, and drug and toxin-induced. Pulmonary hypertension was previously divided into primary and secondary categories; primary pulmonary hypertension described an idiopathic hypertensive vasculopathy exclusively affecting the pulmonary circulation. Whereas secondary pulmonary hypertension was associated with a causal underlying disease process. The histological appearance of lung tissue in each of these conditions is similar and consists of intimal fibrosis, increased medial thickness, pulmonary arteriolar occlusion and plexiform lesions. Recent advances in clinical recognition, classification, and understanding of the underlying pathological processes in pulmonary hypertension have led to improved diagnostic testing and therapeutic options for patients. Clinically, these pulmonary vascular changes initially present as nonspecific symptoms, including unexplained dyspnea on exertion, fatigue, chest pain, and syncope.