In 9 out of 10 cases, pulmonary embolism (PE) begins
as a blood clot in the deep veins of the leg (a condition known as
vein thrombosis). The clot breaks free from the vein and travels through
the bloodstream to the lungs, where it can block an artery.
The animation below shows a blood clot in deep vein
thrombosis. 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 clot in a
deep vein of the leg can break off, travel to the lungs, and block blood
Clots in the leg can form when blood flow is
restricted and slows down. This can happen when you don't move around for long
periods of time, such as:
After some types of surgeries
During a long trip in a car or on an airplane
If you must stay in bed for an extended time
Veins damaged from surgery or injured in other ways
are more prone to blood clots.
Rarely, an air bubble, part of a tumor, or other
tissue travels to the lungs and causes PE. Also, when a large bone in the body
(such as the thigh bone) breaks, fat from the marrow inside the bone can travel
through the blood to the lungs and cause PE.