The pulmonary artery begins at the base of the heart’s right ventricle. It is approximately 3 cm in diameter and 5 cm in length and it eventually divides into the left pulmonary artery and the right pulmonary artery. These arteries then deliver oxygen-depleted blood to each corresponding lung. This is one of the rare arteries that carry deoxygenated blood; the other location is found within the fetus, where the umbilical arteries are. A variety of lung diseases can cause pulmonary hypertension, which is when the blood pressure increases in the pulmonary artery. Pulmonary hypertension can be a consequence or a cause; for example, it may be a consequence of heart disease or a cause of right-ventricular heart failure. Other conditions that may cause pulmonary hypertension include scleroderma and pulmonary embolism. Scleroderma is a chronic systemic autoimmune condition that causes hardening of the skin and connective tissues. A pulmonary embolism occurs when a substance from another place in the body blocks the left or right pulmonary artery.