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Infective endocarditis

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Infective endocarditis is an infection that affects some part of the tissue that lines the inside of the heart chambers (the endocardium). The infection usually involves one or more heart valves which are part of the endocardium. It is a serious infection that is life-threatening.

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In many cases the infection develops quite slowly (over weeks or months). This is sometimes called subacute bacterial endocarditis (SBE). In some cases the symptoms develop quite quickly and you can become very unwell over a few days. The symptoms may include:

  • You tend to feel generally unwell.

  • You may have general aches and pains and tiredness.

  • You may be off your food.

  • A high temperature (fever) develops at some stage in most cases.


Most cases are caused by infection with germs (bacteria). A small number of cases are caused by infection with fungi. To develop this infection, you need to have some bacteria or fungi in the bloodstream. Bacteria or fungi may get into the blood if you have an infection or wound in another part of the body. In particular, dental and mouth infections.

Most bacteria that get into the bloodstream are killed by the immune system. However, sometimes some bacteria survive. They may then settle on a heart valve (particularly if the valve is already damaged in some way), or on another section of the tissue that lines the inside of the heart chambers (the endocardium). Once a small focus of infection develops in the endocardium it is difficult for the immune system to clear it.

In time, small clumps of material called vegetations may develop on infected valves. Fragments of the vegetations may also break off and travel in the bloodstream to other parts of the body.

Endocarditis is uncommon. In the UK it occurs in about 20 in a million people each year. It can occur in anybody but the risk of developing it is increased in people who have:

  • Heart valve problems or an artificial heart valve. Heart valves that are already damaged or abnormal are more likely to become infected.

  • Had surgery to a heart valve.

  • Certain congenital heart defects.

  • A heart condition called hypertrophic cardiomyopathy.

  • Had a previous episode of infective endocarditis.

  • Been injecting street drugs such as heroin, with dirty or contaminated needles.

  • A poor immune system - for example, people with AIDS.

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Complications usually develop if the infection is left untreated or if treatment is delayed. The infection can damage heart valves. This can lead to serious problems such as heart failure. See separate leaflet called Heart Failure.

Small bits may break off from the vegetations on the infected heart valves. These are called infected emboli and get carried in the bloodstream, then lodging in other parts of the body. This can cause various symptoms - for example:

  • Small spots may appear under fingernails, in the eyes or on other parts of the body.

  • Infections may develop in other parts of the body.

  • The spleen may enlarge, as it is the main organ that fights off blood infections.

  • A larger chunk of vegetation may get stuck in an artery in the brain it can cause a stroke or sudden loss of vision in one eye.


You will be admitted to hospital if infective endocarditis is suspected. You will have several blood samples taken which are tested for germs (bacteria) and fungi. If any bacteria are detected in the blood, they are tested against various antibiotics to find which is the best one to use. Some bacteria are resistant to some antibiotics. Therefore, the best antibiotic to use can vary from case to case.

An ultrasound scan of the heart (echocardiography, or 'echo') is the most useful test to confirm infective endocarditis. This test uses reflected sound waves to create an image of the heart. It can detect vegetations and look for damage to heart valves and other heart structures.

Various other tests or scans may be done to find out the extent of the infection and to assess the damage to the heart or other affected organs.

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Antibiotic treatment is all that is required in many cases. However, an operation is needed in up to half of cases when the infection is more severe.


As soon as the condition is suspected you will be given regular doses of antibiotics that are injected directly into a vein. The course of antibiotics is for at least 2-4 weeks but it is often longer. The length of course depends on the germ (bacterium) causing the infection and whether there are complications.

If the cause of the infection is found to be a fungus then antifungal medicines will be given.

If you develop complications to the heart or to other parts of the body, you may need other medication. For example, you may need medicines to counter heart failure or erratic heartbeats, should they develop.


An operation can be life-saving. Operations that may be done include:

  • Replacing a damaged valve with an artificial valve.

  • Valve repair if the damage is less severe and repair is possible.

  • Drainage of any collections of pus (abscesses) that may develop in the heart muscle or in other parts of the body.

What is the outlook?

The outlook (prognosis) is good if the infection is diagnosed and treated early. Many people are cured with a course of antibiotics. However, it is quite common for the infection to be quite advanced before the diagnosis is made and treatment is started. Therefore, serious damage to the heart occurs in some cases. Some people die from the complications.

Further reading and references

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The information on this page is written and peer reviewed by qualified clinicians.

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