A pulmonary embolus is a blood clot that blocks an artery in your lungs. It is a life-threatening problem. Inside the body, blood is normally a fluid. Outside the body blood clots, becoming a solid. The clot may form if you have injured your leg, but often the cause is not known.
Clots tend to break into pieces.
These pieces may float in the bloodstream until they block a blood vessel. A pulmonary embolus is a blood clot that breaks off from the wall of a vein and travels to the lungs. Blood clots may form more easily in your blood vessels if your blood is flowing very slowly through your veins or if disease or medicines you are taking increase the tendency to clot. You have cancer or heart failure or other heart diseases. You have broken a leg or hip.