What is Donald Dewar suffering from?

Following Magnetic Resonance Imaging (MRI scan) and a cardio angiogram - a picture of the coronary arteries - cardiologists at Glasgow Royal Infirmary have diagnosed Mr Dewar as suffering from a leaking aortic valve, a form of heart valve disease.

The aortic valve divides the left ventricle, or chamber, and the aorta - the main artery taking blood from the heart.

What is heart valve disease?

If one or more of the four heart valves are diseased or damaged it can affect the flow of blood in two ways.

If the valve does not open fully, it obstructs the flow of blood - known as valve stenosis. If the valve does not close properly, it will allow blood to leak backwards - called valve incompetence or valve regurgitation.

Both stenosis, which makes the heart pump faster to get blood past the obstruction, and incompetence, which means the heart has to do more to pump the required volume of blood forwards, put extra strain on the heart.

The blood behind the affected valve will also be under increased pressure, called back pressure, leading to a build-up of fluid in the lungs or lower part of the body, depending on the valve affected.

What are the symptoms?

Symptoms include tiredness or breathlessness when exercising, swelling of the ankles and legs, dizziness or fainting in extreme cases, and angina - chest pain - can occur.

What causes it?

Heart valve disease can be caused by being born with one or more abnormal valves, called congenital heart disease.

Disease can also be the result of rheumatic fever, now uncommon in the UK, or ageing of the heart, if valves thicken.

What can be done?

Drugs, including diuretics, ACE inhibitors and digoxin, can be used to treat valvular heart disease, but if the obstruction or leaking of the valves is too severe medicines may not be enough and surgery may be required.

Diseased valves are usually replaced by manufactured valves (artificial/mechanical valves), as in the case of Mr Dewar, or animal valves (tissue valves or biological valves).

Anticoagulants are taken with the valves because there is a risk of blood clots developing on the surface.

Mr Dewar's operation will take two to three hours and he will require a further 10 days in hospital afterwards, followed by a period of recuperation of around 10 weeks.

The operation will involve the surgeon making an incision down the front of his chest and cutting the breastbone lengthways.

His heart will then be stopped and he will be put on a heart-lung bypass machine while the surgeon opens up the heart chamber to reach the valve.

His consultant cardiologist Dr Kerry-Jane Hogg described Mr Dewar's condition as "fairly common" and said the operation would be a "fairly routine procedure".

What are the survival rates?

Long-term survival rates for patients with either artificial or tissue valves are similar.

There is a 5% chance of a patient dying after valve replacement surgery. Risks are less for aortic valve replacement, which Mr Dewar will undergo, and higher for mitral valves.

The danger varies for individual patients depending on factors such as age and other medical conditions.

Endocarditis - infection of the inner lining of the heart cavities - is a possibility and must be treated by intravenous antibiotics.