New Delhi, Jan 24 : Prime Minister Dr. Manmohan Singh is undergoing heart surgery today at the All India Institute of Medical Sciences (AIIMS) in Delhi.

A team of 11 doctors from Asian Heart Institute, Mumbai led by Dr Ramakant Panda, are performing Dr. Singh''s coronary artery bypass graft surgery. The operation is expected to last upto 6- 8 hours.

According to hospital sources, during the surgery, doctors will try to develop an alternate route for the supply of blood by sidelining the blocked part using graft of arteries and vessels derived from other parts of the body.

The coronary artery bypass surgery is performed when arteries get blocked and procedures like angioplasty or medicines fail to clear the blockage.

Surgeons using blood vessels from some other parts of body will create an alternate route by sidelining the blocked part to carry blood.

Dr. Singh was admitted into the hospital on Friday afternoon.

Earlier in the week, the Prime Minister had complained of chest pain and then went through a series of tests where some blockages were found in his arteries.

Dr. Singh underwent a cardiac bypass surgery in 1990 in UK, and angioplasty in Delhi in 2004 in which stents were introduced in his arteries.

Grafts, which were used to bypass the diseased vessel on Dr. Singh 18 years ago, have once again started to narrow.

Meanwhile, President Pratibha Patil has assigned the additional charge of the Ministry of Finance to External Affairs Minister Pranab Mukherjee from today onwards till Dr. Singh recovers after undergoing medical treatment. (ANI)