Commons Speaker Michael Martin has undergone a heart procedure and will be absent from Westminster for a few weeks, his office has said.
Mr Martin was elected to the Commons in 1979
The 60-year-old had an angioplasty procedure, where a tiny balloon is used to open a narrowed coronary artery.
Mr Martin, who is now "recovering well" at home, was admitted to Glasgow Royal Infirmary on 17 February after suffering chest pains.
Party leaders have sent messages wishing him a full and speedy recovery.
The Labour MP for Glasgow North East became Speaker in 2000.
His duties, which include chairing debates in the Commons, will be taken on by deputies Sir Alan Haselhurst, Sylvia Heal and Sir Michael Lord.
In a statement Tony Blair said: "The thoughts of the whole House will be with Michael Martin and his family at this time.
"I wish him a full and speedy recovery and look forward to seeing him back in the House as soon as possible."
Conservative leader David Cameron said: "I was sorry to hear that Michael Martin was unwell and I wish him a speedy recovery and early return to the House of Commons."
And Sir Menzies Campbell, acting leader of the Liberal Democrats, also wished Mr Martin a swift recovery.
"He is held in great affection and respect by all who know him. Our thoughts are with him and his family," said Mr Campbell.
Mr Martin served as deputy Speaker to Betty Boothroyd before being elected to his current role, and has been a Labour MP since 1979.
Before entering politics he was a sheet metal worker and a union official.