The mitral valve (also called the bicuspid valve) separates the upper left heart chamber from the lower left heart chamber, and helps control blood flow through the heart.
Problems with the mitral valve can make the heart less efficient at pumping blood around the body. Severe problems can lead to heart failure if the valve is not surgically repaired or replaced.
This page explains the role of the mitral valve, common problems and how these valve conditions are treated.
How the mitral valve works
During each heartbeat, the smaller upper chambers of the heart (atria) contract to push blood into the larger lower chambers (ventricles).
The mitral valve opens to allow this passage of blood from the left atrium, and closes when the left ventricle is full of blood, to prevent backflow.
When the valve closes, its two leaflets (flaps) normally seal the valve shut. Tendons attached to the leaflets keep them taut and prevent them collapsing through to the other side, or prolapsing.
Mitral valve problems
Common mitral valve problems are:
- mitral regurgitation, or backflow of blood
- mitral valve prolapse, where the valve collapses (often leading to regurgitation)
- mitral stenosis, where the valve doesn't open as wide as it should, restricting blood flow
Any of these three conditions can occur alone or in combination. They are covered in more detail below.
Mitral regurgitation means there is a backflow of blood from the left ventricle to the left atrium when the heart contracts during a heartbeat.
This can happen when the mitral valve leaflets fail to seal shut, either because of problems with the leaflets (such as a mitral valve prolapse – see below) or because of widening of the mitral annulus, which is the ring of muscle surrounding the valve. These problems are more common in older people.
The widening of the mitral annulus can happen when the left ventricle of the heart becomes enlarged, usually because of rheumatic heart disease (a complication of rheumatic fever) or cardiomyopathy, which is an inherited disease of the heart muscle.
If regurgitation is only mild, you may just be monitored at regular intervals with echocardiography (where sound waves are used to create moving pictures of the heart), to check your heart function.
If you have moderate or severe mitral regurgitation, you'll probably need surgery to repair or replace the valve. Read about mitral valve operations.
You may also need treatment (such as drugs to treat atrial fibrillation) for any symptoms, antibiotics to prevent endocarditis (infection of the inner lining of the heart) and medication to prevent blood clots.
Left untreated, moderate to severe mitral regurgitation can lead to congestive heart failure, where the heart can no longer pump enough blood around the body.
Mitral valve prolapse
Mitral valve prolapse means that one or more of the mitral leaflets (flaps) are floppy and don't close tightly, often leading to backflow of blood.
It is usually discovered after an echocardiography is carried out for a different reason (an "echo" uses sound waves to create moving pictures of the heart).
Most people with a mitral valve prolapse will not have symptoms, unless there are complications such as severe mitral regurgitation.
If you have no symptoms and are at low risk of developing severe mitral regurgitation, you won't need any surgical treatment. You may just need to make some lifestyle changes, such as giving up cigarettes, caffeine and alcohol.
You may need to have surgical repair or replacement of the valve if you have:
- severe mitral regurgitation and symptoms
- no symptoms but an enlarged lower heart chamber
- severe mitral regurgiation with atrial fibrillation (a heart rhythm problem) or pulmonary hypertension (high pressure inside the vessels carrying blood from the heart to the lungs)
Repair or replacement of the valve is described in mitral valve operations.
Mitral valve stenosis
Mitral valve stenosis occurs when the valve doesn't open as wide as it should do, leading to the blood flow through the heart being restricted.
Less blood can get to the body, and the upper heart chamber swells as pressure builds up. Blood and fluid collect in the lungs, making it hard for you to breathe.
The most common cause of mitral valve stenosis in adults is rheumatic fever, which can occur 5 to 10 years before the heart valve problems began. Rheumatic fever causes the valve to become inflamed (swollen), and over time the leaflets of the inflamed valve stick together and become scarred, rigid and thickened.
Other causes include calcium deposits forming around the valve, radiation treatment to the chest and some medications, but these are rarer.
Mitral valve stenosis usually happens to patients in their 30s or 40s and may not cause any symptoms. Otherwise, the most common warning signs are:
- breathlessness, such as shortness of breath during activity
- atrial fibrillation (an abnormally fast heart rhythm)
If you don't have any symptoms, your heart function may just be monitored at regular intervals with echocardiography, where sound waves are used to create moving pictures of your heart.
Some patients will need to have treatment for a heart rhythm problem, antibiotics to prevent endocarditis (infection of the inner lining of the heart), and medication to prevent blood clots.
If you have symptoms, you're at risk of heart failure if you do not have an operation either to open up the valve or have it replaced (see mitral valve operations, below). This should also relieve any symptoms, such as breathlessness, prevent endocarditis and reduce the chances of rheumatic fever recurring.
Left untreated, moderate to severe mitral stenosis can lead to congestive heart failure, where the heart can no longer pump enough blood around the body.
Mitral valve operations
If you have a severe case of mitral regurgitation, mitral valve prolapse or mitral valve stenosis, you will need to have a heart valve operation.
Most heart valve operations are performed under general anaesthetic. They usually involve making a cut down the middle of the breastbone, although some surgeons are using smaller incisions (a "minimal access" approach).
Sometimes it's possible to perform the surgery using a "percutaneous" method, which involves feeding a catheter (thin, flexible instrument) into a large vein in your neck or groin and guiding this through to your heart. Patients recover more quickly from this procedure, but the results are less predictable.
The most common procedures are:
- mitral valve repair surgery
- mitral valve replacement surgery
- percutaneous balloon valvuloplasty (used to treat mitral stenosis)
These procedures are briefly explained below, but your surgeon or heart specialist will explain any operation in detail to you, including the risks and benefits.
Percutaneous techniques can also be used for treating mitral prolapse and regurgitation, but they are not covered in any detail here as the methods are still being assessed.
Mitral valve repair surgery
Repairing the mitral valve leaflet is one treatment option for mitral regurgitation.
You will be given a general anaesthetic before an incision is made in your chest to access your mitral valve. The two leaflets of the mitral valve are partially clipped or sewn together, to reduce the amount of blood leaking backwards. It aims to keep the two valve leaflets close together during each heart contraction.
This operation is generally very successful, with a very small chance of major complications.
Mitral valve replacement surgery
Your mitral valve can be surgically replaced with either a mechanical or bioprosthetic valve, which is made from animal tissue.
This is major open heart surgery this is performed under general anaesthetic, and you'll be put on a heart-lung bypass machine.
You'll generally only have a mitral valve replacement if you're unable to have the valve repaired via the above method. You will need it if your valve is furred up with calcium deposits or if the leaflets of your valve do not move.
You will usually need to take medication to prevent blood clots for a long period after this operation.
This operation is generally very successful, with a small chance of major complications.
Percutaneous balloon valvuloplasty
Balloon valvulotomy is a non-surgical treatment option for mitral valve stenosis. It's usually performed by a cardiologist (heart specialist) using just a local anaesthetic.
A catheter is inserted through your skin via a large vein in your groin or neck and passed through to your heart. The tip of the catheter, which has a balloon attached, is positioned directly inside the narrowed valve. The balloon is inflated and deflated several times to widen the valve opening, before the balloon is deflated and removed.
This procedure is most commonly used in young patients who do not have too much calcium deposited on their valve, pregnant women, and patients who are too much at risk from a mitral valve replacement (see above).
Using this type of method is generally less predictable and less reliable than accessing the valve directly, although recovery is generally faster.