Pulmonary embolism is the pathological occlusion of the pulmonary artery. In other words, it is when this big-caliber blood vessel gets clogged up with a thrombus (a clot of blood), microorganisms, such as filaria (parasites) or with foreign matter. The pulmonary artery is the blood vessel that carries deoxygenated blood from the heart right ventricle to the lungs. Thus, in pulmonary embolism, the blood can not be oxygenated and, as a result, the patient dies from asphyxia, that is to say, he smothers to death.
A blood clot is the main cause of pulmonary embolism. It is usually carried in the blood stream by the veins from other parts of the body. It goes through the heart upper and lower chambers without problems, but when it reaches the pulmonary artery, it gets blocked there, occluding it. The symptoms are: difficulty in breathing, chest pain, lung edema (fluids build-up in this organ), tachycardia, high blood pressure, etc.