By Michelle Roberts BBC News Online health staff

Bill Clinton had heart problems

Thousands of patients in the UK undergo this simple technique each year, according to the British Heart Foundation.

BBC News Online looks at what Mr Blair's recuperation is likely to be and the odds of him being 'fighting fit' to serve a third term if elected.

Mr Blair's condition is called supraventricular tachycardia (SVT).

Mr Blair's treatment

It caused by abnormally rapid electrical activity in the upper parts of the heart - the atria.

There are several different types of SVT, and exactly what treatment is best will depend on the particular type of SVT.

In Mr Blair's case, cutting out some of the factors that can trigger the irregular heart beats, such as coffee, alcohol and stress, did not remedy the problem.

CATHETER ABLATION A wire catheter is fed in through a vein in the groin, up to the heart Electrical sensors at the tip of the catheter allow the cardiologist to find the short circuit The catheter then delivers electrical pulses which destroy - ablate - the short circuit

Sometimes drugs are not effective in controlling the abnormal rhythm either and other treatments can be tried.

Last year, Mr Blair had a procedure called cardioversion, which uses a small electric shock to make the heartbeat return to normal.

But the problem has persisted and now Mr Blair has undergone a procedure called catheter ablation.

This does not involve a surgical incision and will be carried out under local anaesthetic and sedation.

A catheter - a long, thin wire - is introduced through the skin into a large vein in the leg and manoeuvred up to the heart under x-ray guidance.

Success rate

When the tip of the catheter is lying at the correct place inside the heart chambers pulses of radio frequency energy are generated to destroy or ablate the area causing the abnormal rhythm.

A 95% success rate would be expected Cardiologist Dr Andrew Grace

Patients having the same heart procedure as Tony Blair could wait up to nine months for treatment but most are seen within two, according to the British Cardiac Society and the British Heart Foundation.

One of the country's leading cardiologists, Dr Andrew Grace of Papworth Hospital, said there was a high success rate with this "very safe, effective and well tolerated" procedure.

He told the BBC Radio 4 Today programme: "In general terms, with the simpler forms of abnormality, then a 95% success rate would be expected with a simple, short procedure from which one would expect the patient to recover rapidly."

In the other 5%, the procedure can be repeated, he said.

In some cases, the abnormal rhythm may persist or come back again.

There are other options for such patients, including pacemakers and drug therapies, he said.

Recuperation

Belinda Linden, head of medical information at the British Heart Foundation, said most people who have the procedure tend to stay overnight in hospital to check everything has gone well.

There should be no reason why people can't continue their usual activity Belinda Linden of the British Heart Foundation

"For the first day afterwards you tend to take things easily, partly because you have had a catheter treatment.

"There may be some bruising and discomfort around the site where the catheter went in.

"Generally, you can go back to work a couple of days later. But they suggest you don't drive for about a week."

She said there was a very small risk of stroke with the procedure, but this tended to be in older people with other underlying medical problems.

"The interesting thing about a heart rhythm abnormality is that it does not necessarily suggest there is any abnormality of the heart itself.

"So once the rhythm is corrected, there should be no reason why people can't continue their usual activity whether it be walking, running or cycling."

Life-long risk?

Ms Linden said it was possible Mr Blair had inherited his abnormal heart rhythm. His father suffered a stroke at the age of 40.

But she said there were many possible causes, including stress.

"Usually, it's not down to stress but if you find you are overworking, you are running around, rushing and are very anxious you have more adrenaline running around your system.

"Therefore, although the cause of the abnormal rhythm is unlikely to be stress, sometimes it can trigger a fast heart beat where before it may not have."

Part of running a country?

Last month, former US President Bill Clinton underwent a five-hour quadruple heart bypass operation to relieve clogged arteries.

But Ms Linden said this was completely different to Mr Blair's illness.