What is a pulmonary embolism and what causes it?

A pulmonary embolism happens when a blood vessel in your lungs becomes blocked, usually with a blood clot. It can be very serious because the blockage can stop blood going to parts of your lungs. Fast medical treatment can save your life.

What’s the difference between an acute pulmonary embolism and a chronic pulmonary embolism? 

An acute pulmonary embolism is when there’s a sudden blockage in the blood vessel in your lungs.

A chronic pulmonary embolism is when the blood vessels in your lungs have been blocked for a longer amount of time. Most commonly this happens if you have had an acute pulmonary embolism before and the previous blood clots have not dissolved completely after treatment.

Our information is about acute pulmonary embolisms.

Pulmonary embolism – a blockage in a blood vessel in your lungs, usually caused by a blood clot that has travelled from your veins.

Deep vein thrombosis (DVT) – a blood clot in a deep vein, usually in your leg.

Blood clot – a clump of blood formed in a blood vessel.

A pulmonary embolism is usually caused by a blood clot travelling up to your lungs from one of the deep veins in your body. A deep vein is a larger vein that is found deep within your body, rather than the smaller veins closer to your skin. This kind of blood clot is called a deep vein thrombosis (DVT). A DVT usually starts in your leg, but you can also develop one in your arm or stomach. The NHS has more information about DVT.

A pulmonary embolism can also be caused by air, fat or tumour cells in your lungs. But this is very rare.

Sometimes, your healthcare professional may be unable to find the cause of a pulmonary embolism. This can be called an ‘unprovoked’ pulmonary embolism.

Pulmonary embolisms aren’t very common. Around 99 in 100,000 people are diagnosed with a pulmonary embolism each year.