An embolism (EM-bo-liz-um) is a blockage in the bloodstream caused by a blood clot * , air bubble, fatty tissue, or other substance that plugs a blood vessel.

An embolism in an artery. An embolism blocking blood flow through an artery may be a serious problem.

An embolism in an artery. An embolism blocking blood flow through an artery may be a serious problem.
Illustration by Frank Forney. © 2016 Cengage Learning®.

What Is an Embolism?

The body's circulatory system * is like a huge network of small roads and large interstate highways. It is important that blood flows continuously throughout the body to carry nutrients, oxygen, and other substances to cells and organs. But, like traffic on a highway, sometimes a part of the circulatory system can become blocked.

An embolism is a blockage that plugs up a blood vessel and slows or even stops blood flow to the area of the body supplied by the artery * . Many substances can cause blockages. Usually, the embolus (EM-bo-lus) is something small that has broken free from another part of the body and travels through the bloodstream until it gets jammed in a blood vessel that is too narrow for it to pass freely.

Emboli (EM-bo-ly), which is the plural of embolus, may be life-threatening. They may cause death if they block a major artery, such as the large pulmonary artery that runs through the lungs. They also may cause death of body tissue if they prevent blood flow to a given area.

The most common type of embolism results from the clotting of blood. When blood clots form inside blood vessels, by a process called thrombosis * , they may break free and travel to the pulmonary artery. The pulmonary artery carries blood from the right side of the heart into the lungs. In the lungs, blood disposes of carbon dioxide and picks up more oxygen. When blood clots get stuck in the pulmonary artery, they prevent blood from picking up oxygen. This condition is a medical emergency that causes symptoms similar to a heart attack.

Thrombophlebitis (throm-bo-fluh-BI-tis) can occur when a blood clot causes inflammation inside a vein (usually in the legs). If the clot forms in a vein in muscle, it causes what is known as deep-vein thrombosis (DVT). A DVT may break free and become an embolus that travels inside the blood vessel to the lungs, and this eventually may cause a blockage of the pulmonary artery inside the heart. When this occurs, it is called a pulmonary embolism.

The following substances, although less common, may cause embolism:

An embolism may occur in any artery. However, it occurs often in the pulmonary arteries because all the blood returning to the heart from the body is pumped through the pulmonary arterial system first.

How Common Is an Embolism?

Pulmonary emboli develop in 200,000 to 3 million Americans each year, and up to 10 percent die within the first hour. Embolisms are not contagious.

How Do People Know They Have an Embolism?

Symptoms of a pulmonary embolism may include chest pain that may feel worse when breathing deeply, shortness of breath, coughing or coughing up blood, dizziness, sweating, rapid breathing, and rapid heartbeat. These symptoms are similar to those of a heart attack. Sometimes an embolism does not cause any symptoms at all.

How Do Doctors Diagnose and Treat an Embolism?


Doctors may use blood tests, an x-ray, a CT scan * Treatment

With immediate treatment, many people are saved from a fatal embolism and lead a normal life. Doctors may use drugs that dissolve the embolism and prevent others from forming. Doctors may extend the use of drug therapy or consider surgery to insert a filter to catch clots in individuals with multiple chronic pulmonary emboli.

Can an Embolism Be Prevented?

Exercise, weight loss (if needed), and a proper diet can help prevent emboli from forming.

See also Anemia, Bleeding, and Clotting • Bends • Phlebitis and Venous Thrombosis


Books and Articles

England, Tim, and Akhtar Nasim, eds. ABCs of Arterial and Venous Disease. London, UK: BMJ Books, 2014.

Greener, Mark. The Stroke Survival Guide. London, UK: Sheldon Press, 2015.


MedlinePlus. “Pulmonary Embolus.” U.S. National Library of Medicine, National Institutes of Health. https://www.nlm.nih.gov/medlineplus/ency/article/000132.htm (accessed March 24, 2016).

National Heart, Lung, and Blood Institute. “What Is Pulmonary Embolism?” http://www.nhlbi.nih.gov/health/health-topics/topics/pe/ (accessed March 24, 2016).

Society for Vascular Surgery. “Pulmonary Embolism.” Vascular Web. https://vascular.org/patient-resources/vascular-conditions/pulmonary-embolism (accessed March 24, 2016).


National Blood Clot Alliance. 110 North Washington St., Suite 328, Rockville, MD 20850. Toll-free: 877-4-NO-CLOT. Website: http://www.stoptheclot.org (accessed March 24, 2016).

National Heart, Lung, and Blood Institute. PO Box 30105, Bethesda, MD, 20824-0105. Telephone: 301-592-8573. Website: http://www.nhlbi.nih.gov (accessed March 24, 2016).

* blood clot is a thickening of the blood into a jellylike substance that helps stop bleeding. Clotting of the blood within a blood vessel can lead to blockage of blood flow.

* circulatory (SIR-kyoo-luh-tor-e) system is the system composed of the heart and blood vessels that moves blood throughout the body.

* artery is a vessel that carries blood from the heart to tissues in the body.

* thrombosis is the formation or development of a blood clot or thrombus.

* tumor (TOO-mor) is an abnormal growth of body tissue that has no known cause or physiologic purpose. A tumor may or may not be cancerous.

* CT scans, computed tomography (to-MOG-ra-fee) scans, or CAT (computerized axial tomography) scans, use computers to view structures inside the body.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)