Infective Endocarditis

Authored by , Reviewed by Dr Adrian Bonsall | Last edited | Certified by The Information Standard

Infective endocarditis is an infection that affects some part of the tissue that lines the inside of the heart chambers (the endocardium).

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.

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. The blood usually does not contain any bacteria or fungi. However, some may get into the blood if you have an infection or wound in another part of the body. In particular, dental and mouth infections are situations where bacteria can quite easily get into the bloodstream.

People who inject street drugs may also inject bacteria or fungi into their bloodstream if they use dirty or contaminated needles.

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. The vegetations contain bacteria or fungi, small blood clots and other debris from the infection. The vegetations may prevent affected valves from opening and closing properly. The infection can also damage affected valves and may spread to other areas of the endocardium or heart tissue. 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.

If you have an increased risk of developing infective endocarditis, do report promptly to your doctor any symptoms that you think may be due to infective endocarditis. The earlier the condition is diagnosed and treated, the better the likely outcome.

Slowly developing infection

In many cases the infection develops quite slowly. This is sometimes called subacute bacterial endocarditis (SBE). Symptoms can develop gradually (over weeks or months) and can be vague at first. 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. As these first symptoms can be caused by a lot of other conditions, the cause of the symptoms may not be diagnosed for some time.

Heart murmurs tend to develop

These are sounds that can be heard by a doctor listening to your heart with a stethoscope. Murmurs are caused by abnormal flow of blood through faulty or damaged valves. If you already have a heart murmur from an existing valve problem, the murmur may change or become more intense. A new or changing murmur is often what alerts a doctor to suspect infective endocarditis

Rapidly developing infection

In some cases the symptoms develop quite quickly and you can become very unwell over a few days. The speed at which the illness develops partly depends on which germ (bacterium) or fungus is causing the infection. Some bacteria are more aggressive (virulent) than others.

Complications usually develop if the infection is left untreated or if treatment is delayed.

Complications in the heart

The infection can damage heart valves. This can lead to serious problems such as heart failure. See separate leaflet called Heart Failure. In some cases, the infection spreads and can damage other parts of the heart. For example, the infection may spread to affect the electrical (conducting) system of the heart and cause the heartbeat to become erratic. In some cases, a ball of pus (an abscess) forms in the heart muscle nearby.

Complications in other parts of the body

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.
  • If a larger chunk of vegetation breaks off then it can block the blood flow in a main blood vessel (artery). For example, if it gets 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.

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. Sometimes the type of antibiotics is changed once the results of the blood samples are back and the best antibiotics to use are found. 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.

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.

If you inject street drugs

Your risk of infective endocarditis can be reduced by always using a clean needle and other injecting equipment when injecting street drugs.

Dental health

Good oral hygiene and dental hygiene are also thought to be important. In particular, if you have any condition which increases your risk of developing infective endocarditis (see above) then don't let any dental problems go untreated. Such conditions include a dental abscess or gum disease. These dental conditions increase the chance of germs (bacteria) getting into the bloodstream.

If you have dental and surgical procedures

Until early 2008, it had been usual medical practice to advise people with an increased risk of developing infective endocarditis to take a short course of antibiotics (antibiotic cover) during certain procedures. These included:

  • Various dental procedures.
  • Looking into the stomach (endoscopy).
  • Looking into the bowel (colonoscopy).
  • Looking into the bladder (cystoscopy).

The logic was that these procedures might push some germs (bacteria) into the bloodstream. It was thought that antibiotic cover would kill bacteria that get into the blood before they settle on the endocardium or heart valves.

However, in March 2008 the National Institute for Health and Care Excellence (NICE) in the UK published new guidance on the use of antibiotic prophylaxis (antibiotic cover) against infective endocarditis. This recommended an end to the practice of prescribing antibiotics for at-risk patients during dental and other procedures. NICE recommends that you should now only be offered antibiotic cover if the procedure is at a site where there is already a suspected infection. The reason for this change in practice is because NICE found that research studies do not support the use of antibiotics to prevent infective endocarditis during dental or other procedures. Also, taking antibiotics carries its own risk (such as side-effects and sometimes serious reactions to antibiotics).

However this NICE guideline is controversial. The European Society of Cardiology guidelines in 2015 recommend that antibiotic prophylaxis be given to people with the highest risk of developing infective endocarditis. Your own doctor or dentist will advise for your own particular circumstance.

Further reading and references

  • ; 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease. Circulation. 2017 CIR.0000000000000503. Originally published March 15, 2017.

  • ; European Society of Cardiology (Aug 2015)

  • ; NICE Clinical Guideline (March 2008)

  • ; Guidelines on the management of valvular heart disease: The Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology, 2017.

  • ; What is new in ACC/AHA 2017 focused update of valvular heart disease guidelines. Anatol J Cardiol. 2017 Jun17(6):421-422. doi: 10.14744/AnatolJCardiol.2017.7925.

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