Endocarditis is caused by bacteria in the bloodstream multiplying and spreading across the inner lining of your heart (endocardium). The endocardium becomes inflamed, causing damage to your heart valves. Your heart is usually well protected against infection so bacteria can pass harmlessly by.

But if your heart valves are damaged or you have an artificial valve, it's easier for bacteria to take root and bypass your normal immune response to infection.

Small clumps of bacteria can develop at the site of the infection. There's a risk of these clumps acting in a similar way to blood clots, travelling away from the heart and blocking the blood supply to the organs. This can cause organ failure or trigger a stroke.

How bacteria reach the heart

There are several ways that bacteria can enter your blood.

Mouth

Everyday activities, such as brushing your teeth or chewing your food, can sometimes allow bacteria to enter the bloodstream. The risk is increased if your teeth and gums are in bad condition because it makes it easier for bacteria to enter.

Infection

Bacteria can spread from the site of a pre-existing infection, such as a skin infection or gum disease.

Needles and tubes

Any medical procedure that involves placing a medical instrument inside the body carries a small associated risk of introducing bacteria into your bloodstream.

Who's at risk

There are a number of things that can make your heart more vulnerable to infection and increase your chance of developing endocarditis. These include:

• heart valve disease
• having prosthetic valves
• hypertrophic cardiomyopathy
• injecting drugs
• congenital heart disease
• you've had endocarditis before

Prosthetic valves

The prosthetic (artificial) valves used in aortic valve replacement surgery replace heart valves that have been damaged by heart valve disease. But bacteria can also take root around prosthetic valves, which can occasionally trigger endocarditis.

Fungal endocarditis

Endocarditis caused by a fungal infection is rarer than bacterial endocarditis, and usually more serious. You're more at risk of fungal endocarditis if you:

• inject drugs
• have a history of heart surgery
• have a central venous catheter – a tube connected to a vein in the neck, groin or chest, which is used to deliver medicines or fluids to people who are seriously ill
• have a weakened immune system