Tony Blair may be "100 per cent recovered", according to his political spokesman, but doctors warned yesterday that his heart problems could recur.
Experts said there was a possibility the Prime Minister might need further, more invasive treatment if he suffers similar symptoms again.
The condition, called supra- ventricular tachycardia, causes irregular heartbeats and shortness of breath.
Yesterday, Mr Blair was sedated for 20 minutes and given cardioversion treatment, which uses a small electric shock to correct the irregular heartbeat.
He may also have been fitted with a device to monitor his heartbeat during the next 48 hours to check whether it returns to normal.
Sir Charles George, medical director of the British Heart Foundation, said: "There is a possibility this might recur. If it were to recur, he would need further tests to investigate what was happening."
Sir Charles said further tests could include electro-physical investigations, in which tiny wires are passed through the groin to measure electrical abnormalities around the heart. If a problem was detected, a radio frequency wave would then be used to "fry" the area causing the irregular heartbeat.
Despite advice from his doctors to rest for 24 hours, Mr Blair chaired a series of meetings from early yesterday morning. However, heart experts said returning to work so quickly carried no risks.
"He is not going to come to any harm by chairing meetings, and I would imagine it would be quite hard for him, with everything that is going on, to say he was going to take a back seat," said Sir Charles. "If he feels well and wants to work, there is no point in enforcing bed rest."
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