The pulmonary embolism (PE) process was first described by Rudolph Virchow, the famous nineteenth-century German pathologist who called the traveling clots embolia. The terms   "embolus" (plural: emboli) and "embolism" are still used to describe a clot or part of a clot that has formed in one site and traveled to another part of the body. When a clot wedges itself in one of the pulmonary arteries or its branches, it is called PE.

A very large PE can block the entire trunk of the pulmonary artery (before it branches into the right and left pulmonary arteries) and cause death instantly. Pulmonary emboli that are not quite so large may block an entire right or left pulmonary artery, stopping the blood flow to an entire lung and-especially if the person already has lung or heart disease-causing death. Smaller emboli may block smaller branches of the pulmonary artery with varying consequences. When the blood supply to a small "end-artery" at the edge of the lung is blocked, oxygen to that part of the lung is cut off, and the cells in that part of the lung begin to die, resulting in  pulmonary infarction (that is, death of lung tissue). When blood flow is blocked within a larger branch of the pulmonary artery, the normal exchange of oxygen for carbon dioxide does not take place and the entire body is affected. Pulmonary infarctions usually result from smaller clots and are unlikely to be fatal.

The likelihood of death from PE depends largely on the size of the PE. If the main pulmonary artery is completely blocked, the right ventricle (the chamber of the heart that pumps blood into the lungs) cannot get the blood into the lungs; this "right ventricular failure" then leads to death from PE. The age and health of the affected individual are also critical factors. When the person already has lung or heart disease, PE may have a more dramatic impact. While the death rate from PE may be as high as 25 percent in sick, hospitalized patients, the death rate in young healthy individuals is closer to 1 percent.

Symptoms of Pulmonary Embolism
Symptoms usually begin suddenly and may include:
Sudden shortness of breath.
Sharp chest pain, often aggravated by coughing or movement.
Pain in your back.
Cough with or without bloody sputum.
Excessive sweating.
Rapid pulse or breathing.
Lightheadedness or passing out.
Blue lips or nail beds.