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What Causes Pulmonary Embolism?
Major Causes
Pulmonary embolism (PE) usually begins as a blood clot in a deep vein of the leg. This condition is called deep vein thrombosis. The clot can break free, travel through the bloodstream to the lungs, and block an artery.
The animation below shows how a blood clot from a deep vein in the leg can travel to the lungs, causing pulmonary embolism. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how a blood clot in a deep vein of the leg can break off, travel to the lungs, and block blood flow.
Blood clots can form in the deep veins of the legs if blood flow is restricted and slows down. This can happen if you don't move around for long periods, such as:
- After some types of surgery
- During a long trip in a car or airplane
- If you must stay in bed for an extended time
Blood clots are more likely to develop in veins damaged from surgery or injured in other ways.
Other Causes
Rarely, an air bubble, part of a tumor, or other tissue travels to the lungs and causes PE. Also, if a large bone in the body (such as the thigh bone) breaks, fat from the bone marrow can travel through the blood. If the fat reaches the lungs, it can cause PE.
Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Pulmonary Embolism, visit www.clinicaltrials.gov.
The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.
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