"Two more grafts are left. The operation is still on," Vaishnav said.

Prime Minister Manmohan Singh was wheeled into the operation theatre at 5:30 am. The operation finally began at 7:15 am, Vaishnav said.

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He said an 11-member team from the ASI led by Dr Ramakant Panda was performing the operation on the 76-year-old leader at the All India Institute of Medical Sciences (AIIMS) here. The team comprises three more doctors and the rest are support staff.

Heart bypass, which the Prime Minister had undergone 18 years ago in London, involves grafting of veins or arteries from elsewhere in the patient's body to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation supplying the heart muscle.

Six years ago, Singh had also undergone an angioplasty.