what's cause blood clot in the lung?
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.