A pulmonary embolism is a blockage in the pulmonary artery, which is the blood vessel that transports blood from the heart to the lungs.

This blockage - usually a blood clot - is potentially life-threatening because it can prevent blood from reaching your lungs.

The symptoms of a pulmonary embolism can sometimes be difficult to recognise because they can vary between individuals. However, the main symptoms include:

  • chest pain - a sharp, stabbing pain that may be worse when you breathe in
  • shortness of breath - which can come on suddenly or develop gradually
  • coughing - which is usually dry but may include coughing up blood or mucus that contains blood
  • feeling faint, dizzy, or passing out

You should visit your GP immediately if you have a combination of these symptoms.

If your symptoms are particularly severe, dial 999 immediately and ask for an ambulance.

Read more about the symptoms of a pulmonary embolism.

Causes of a pulmonary embolism

A pulmonary embolism is often caused by a blood clot travelling up from one of the deep veins in your legs to your heart and lungs.

A blood clot in one of the deep veins of the legs is known as deep vein thrombosis (DVT). DVT can occur for no apparent reason, but it often develops after long periods of inactivity, such as during a long-haul flight or if you're ill in hospital.

DVTs can also occur during pregnancy, as a result of some medical conditions, such as cancer or heart failure, or if the wall of a blood vessel becomes damaged.

Read more about the causes of a pulmonary embolism.

Diagnosing a pulmonary embolism

Diagnosing a pulmonary embolism can be difficult because the symptoms are common to many other conditions. However, an accurate diagnosis is important because treating a pulmonary embolism isn't always easy and the treatment used can cause side effects.

A number of tests can help determine whether you have a pulmonary embolism or rule out other causes of your symptoms. For example, you may have a chest X-ray or tests to check how well your lungs are working.

Treating a pulmonary embolism

Pulmonary embolisms are treated with anticoagulant medicines. These stop the blood clot getting bigger while your body slowly reabsorbs it, and reduce your risk of further clots developing.

If you're diagnosed with a pulmonary embolism, you'll usually be given regular anticoagulant injections for about five days to begin with. You'll also be prescribed an anticoagulant tablet called warfarin to take for several months.

As part of your treatment, you will also need to have regular blood tests to check that the dose of warfarin you are receiving is correct. If it is too high, you may experience bleeding, and it is too low you may have further blood clots.

Keeping mobile will also help you to maintain good blood circulation and prevent further blood clots from forming.

Read more about treating a pulmonary embolism.

Preventing a pulmonary embolism

There are a number of methods that may be recommended to prevent a pulmonary embolism if you are at risk of developing blood clots.

These include:

  • taking anticoagulant tablets, such as warfarin
  • wearing compression stockings or using compression devices
  • avoiding prolonged periods of inactivity
  • a healthy lifestyle – such as stopping smoking (if you smoke) and eating a healthy, balanced diet that is low in fat and includes plenty of fruit and vegetables

Read more about preventing a pulmonary embolism.

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Signs and symptoms of a pulmonary embolism (a blockage in the artery to the lungs) include chest pain, shortness of breath and coughing.

Recognising the signs and symptoms of a pulmonary embolism can be difficult because they can vary between individuals. Small clots may cause no noticeable symptoms.

Symptoms of a pulmonary embolism can include:

Many pulmonary embolisms are caused by a blood clot in the leg, known as a deep vein thrombosis (DVT), travelling towards the lungs. Some people with a pulmonary embolism therefore also have symptoms of DVT, such as pain, redness and swelling in one leg (usually the calf).

Seeking medical help

You should visit your GP as soon as possible if you experience any combination of the above symptoms. If it is not possible for you to visit your GP, you can call NHS Direct Wales on 0845 4647 or you can contact your local out-of-hours service.

Dial 999 immediately to ask for an ambulance if your symptoms are severe.

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A pulmonary embolism occurs when the artery that carries blood to the lungs becomes blocked.

The blockage is usually a blood clot, although it can be a fat droplet, an air bubble or amniotic fluid (fluid that surrounds unborn babies).

If it's a blood clot, this will have usually come from one of the deep veins in your legs and is known as deep vein thrombosis (DVT).

The main reasons why blood clots develop are outlined below.


If you're inactive, blood tends to collect in the lower parts of your body, particularly in your lower legs. This isn't usually a problem because when you start to move, your blood flow increases and blood begins to move evenly around your body.

However, if you're immobile for a long time, the flow of blood around your body can slow down considerably. You're likely to be immobile:

  • after a serious illness such as a stroke
  • after an injury or operation
  • when travelling on a long journey by plane, train or car

If your blood flow slows down because of a long period of inactivity, your risk of developing a blood clot increases.

Blood vessel damage

If a blood vessel is damaged, the inside of the blood vessel can become narrowed or blocked. This can result in a blood clot forming.

Blood vessels can be damaged by injuries such as broken bones or severe muscle damage. If a blood vessel is damaged during surgery, a blood clot may develop, particularly in operations carried out on the lower half of the body.

Conditions such as vasculitis (inflammation of the wall of a blood vessel) and some types of medication, such as chemotherapy medication, can also cause blood vessel damage.

Blood that clots too easily

Your risk of developing a pulmonary embolism is increased if you have a condition that causes your blood to clot more easily than normal.

Conditions that increase the likelihood of your blood clotting include:

  • cancer (cancer treatments, such as chemotherapy and radiotherapy, can also make blood clotting worse)
  • heart failure
  • thrombophilia - an inherited condition where a person's blood has an increased tendency to form clots
  • antiphospholipid syndrome (an immune system disorder that causes the blood to become abnormally sticky, increasing its tendency to clot)

Other risk factors

Other factors that increase your risk of developing a pulmonary embolism include:

Your chances of developing a blood clot are very small if you're taking the contraceptive pill or HRT, and your GP will usually assess your individual risk before prescribing either medication.

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It can sometimes be difficult to diagnose a pulmonary embolism because the symptoms vary between individuals and are similar to many other conditions.

Around half of all people who develop a pulmonary embolism do so while they're in hospital.

The condition may be suspected if:

  • you have one or more associated risk factors, such as being over 60 years of age or having a previous blood clot
  • you have a blood clot in one of your legs, known as a deep vein thrombosis (DVT)
  • there is no other likely explanation for your symptoms

It's important that pulmonary embolisms are diagnosed correctly because treating them isn't always easy and the treatments used can cause side effects.


A number of tests may be used to help determine if you have a pulmonary embolism or to rule out other causes of your symptoms.

For example, you may have a chest X-ray or tests to check how well your lungs are working. You may also have some of the more specialised tests discussed below.

Blood tests

Blood tests can be carried out to detect a number of signs of pulmonary embolism. One of the main tests looks for a substance called D-dimer

D-dimer is a protein that is found in the blood after a blood clot has broken down. A D-dimer test can be used to help diagnose blood clotting abnormalities, such as thrombosis (where a blood clot develops in a blood vessel).

If your blood test result indicates high levels of D-dimer, it suggests that pieces of blood clot are loose in your bloodstream and may have become lodged in your pulmonary artery.

Computerised tomography pulmonary angiography

Computerised tomography pulmonary angiography (CTPA) is a procedure where you're injected with a special dye before having a CT scan.The dye makes it easier to see the blood vessels in your lungs during the scan.

A CT scan involves taking a series of X-rays to create a highly detailed image of the inside of your body. If there's a pulmonary embolism in one of your lungs, it may show up on the scan as a gap in your blood supply.

Ventilation-perfusion scan

A ventilation and perfusion scan is used to examine the flow of air and blood in your lungs.

Before having the scan, you'll be asked to inhale a tasteless, odourless and slightly radioactive gas through a mouthpiece. The gas helps highlight the air flow in your lungs during the scan.

You'll also be given an injection that contains a small amount of radioactive material to highlight the blood vessels in your lungs during the scan.

If the scan shows parts of your lungs have air in them but no blood supply, it may be the result of a pulmonary embolism.

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The main treatment for a pulmonary embolism is an anticoagulant, a type of medication that stops your blood clotting easily.

The anticoagulant will prevent the clot getting larger while your body slowly absorbs it. It also reduces the risk of further clots developing.

In some cases, other treatments may be needed to remove or break up the clot. This can be done with medication called thrombolytics or, less commonly, surgery.

About half of all cases of pulmonary embolism occur in hospital. If you're not already in hospital, you'll be admitted so you can receive treatment. If necessary, you'll be given oxygen to help you breathe more comfortably.


Anticoagulants are often referred to as blood-thinning medicines, although they don't actually thin the blood. Instead, they alter chemicals in the blood to prevent clots forming easily.

The main anticoagulants used to treat pulmonary embolisms are heparin and warfarin.


Heparin is given as an injection. Regular injections of this medication are usually used as the initial treatment for a pulmonary embolism because they start working immediately.

Most people diagnosed with a pulmonary embolism will initially need injections of heparin for at least five days. You'll then usually continue taking warfarin only.

Heparin can cause side effects, including:


If you're diagnosed with a pulmonary embolism, you'll usually start taking warfarin tablets after you've have the initial injections of heparin.

Warfarin takes longer to start working than heparin injections, but as it's more convenient to take, it's usually recommended for a longer period after you stop having the injections.

Treatment with warfarin will usually be recommended for at least three months, although some people need to take it for longer than this. Occasionally, warfarin may need to be taken for the rest of your life.

The effects of warfarin vary from person to person, so you'll need to be closely monitored and have regular blood tests to check you're taking the right dosage. These tests can usually be carried out on an outpatient basis, which means you won't need to stay in hospital.

You may need two or three blood tests a week when you first start taking warfarin until the correct dose is determined. After this, you may only need to have a blood test about once a month.

There are several factors that can alter the effectiveness of warfarin, including your diet, other medications you're taking and how well your liver is working.

Therefore, while taking warfarin you should:

  • try to keep your diet consistent
  • limit your alcohol consumption and avoid drinking more than the recommended amounts
  • take your medication at the same time each day
  • avoid taking any other medicine without first checking with your GP, pharmacist or anticoagulant specialist
  • avoid taking herbal medicines

Warfarin can cause a wide range of side effects, including:

Read more about the side effects of warfarin.


Dabigatran is an oral anticoagulant that specifically targets thrombin (a protein that helps blood clots form). It's used to treat and prevent deep vein thrombosis (DVT) and pulmonary embolism in adults.

The recommended dosage of dabigatran will depend on your age and whether you're taking other medication for other health conditions. Dabigatran isn't recommended for people with severely reduced kidney function.

Bleeding and indigestion are the most common side effects of dabigatran.

Read the National Institute for Health and Care Excellence (NICE) guidance about dabigatran for the treatment and secondary prevention of deep vein thrombosis and pulmonary embolism (PDF, 255kb).


Rivaroxaban is another medication that can be used to treat and prevent DVT and pulmonary embolism in adults.

The recommended dosage of rivaroxaban will depend on whether it's being used to treat pulmonary embolism for the first time or a recurrence of the problem. How long treatment lasts will depend on a person's bleeding risk and other clinical criteria.

Side effects of rivaroxaban can be varied and may include anaemia, dizziness, headache, fainting, rapid heartbeat (tachycardia), low blood pressure, diarrhoea, constipation and swelling, particularly of the ankles and feet (oedema).

Read the NICE guidance about rivaroxaban for treating pulmonary embolism and preventing recurrent venous thromboembolism (PDF, 233kb).


Apixaban is another anticoagulant that's recently been approved by NICE to treat and prevent DVT or pulmonary embolism.

It's taken orally (in tablet form) twice a day for the first seven days. The dosage is then halved and taken twice a day for at least three months.

The most common side effects of apixaban are bleeding, bruising, nausea and anaemia. It's also recommended that apixaban should be used with caution in people with severe kidney problems.

You can read more about apixaban for the treatment and secondary prevention of deep vein thrombosis and pulmonary embolism (PDF, 228kb).

Special considerations

If you're pregnant, you'll be given regular heparin injections instead of warfarin tablets for the full length of your pregnancy. This is recommended because taking warfarin tablets while you're pregnant could harm your baby.

If you have cancer, you'll usually be given heparin injections instead of warfarin tablets for six months or until the cancer is cured. Evidence suggests that regular injections are more effective than warfarin tablets in these cases.

Removing the blockage

In more severe cases of pulmonary embolism, treatment may be needed to remove the blockage. This is often achieved using injections of a type of medication called a thrombolytic, such as alteplase, which breaks up the blood clot.

A newer procedure may also be used called ultrasound-enhanced, catheter-directed thrombolysis. It involves using high-frequency, low-energy ultrasound waves in combination with thrombolytic medication to dissolve the blood clot. The procedure usually lasts for 12-24 hours and you'll be continuously monitored throughout the duration of the treatment.

Read NICE guidelines on ultrasound-enhanced, catheter-directed thrombolysis for pulmonary embolism (PDF, 136kb).

Occasionally, a surgical procedure called an embolectomy may be used to treat a pulmonary embolism. This is where a surgeon makes a cut in the pulmonary artery and the blockage is sucked out. However, this is a major operation so it's usually only recommended in particularly severe cases or if other treatments are unsuitable.

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If you are at risk of developing blood clots, there are a number of things that may be recommended to help prevent a pulmonary embolism.


If you are admitted to hospital to have surgery, your care team may recommend that you take an anticoagulant such as warfarin during your stay in hospital and when you go home.

This medication alters chemicals in your blood so that clots don't form easily.

Compression stockings

It may also be recommended that you wear compression stockings and use compression devices while you are in hospital and after you go home. Compression stockings fit tightly around your lower legs and encourage your blood to flow more quickly around your body. Compression devices are inflatable and work in a similar way, expanding at regular intervals to squeeze your legs and encourage the flow of blood.

Increasing mobility

Pulmonary embolisms can sometimes occur when the blood flow slows down during a prolonged period of inactivity, such as during recovery from surgery or long-distance travel.

It is therefore very important that you increase your mobility as soon as possible after surgery by moving around or doing leg exercises. You should also avoid taking long journeys for four weeks after you come out of hospital.

If you are at risk of developing blood clots, consult your GP before embarking on long-distance travel. They can offer advice about ways to reduce the chances of a clot developing during your journey, such as:

  • perform simple leg exercises, such as regularly flexing your ankles
  • take occasional short walks when possible
  • take advantage of refuelling stopovers, where it may be possible to get out and walk about
  • wear elastic compression stockings

Read more about preventing blood clots when you travel.

Smoking, diet and exercise

You can also reduce your risk of developing a pulmonary embolism by:

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Selected links

NHS Direct Wales links

Deep vein thrombosis

External links

British Lung Foundation: you and your lungs


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The information on this page has been adapted by NHS Wales from original content supplied by NHS Choices.
Last Updated: 13/01/2016 12:27:01