Bahujan Samaj Party chief Kanshi Ram underwent heart surgery at a hospital in New Delhi on Monday and his condition was critical, doctors attending on him said.
Ram, admitted to the Batra Hospital for the last eight months due to heart problems, was operated upon on Tuesday for a block in an artery.
He had been put on ventilator after the coronary artery bypass surgery, the doctors said.
The BSP leader has been suffering from heart problem for several years and an angioplasty was done on him in 1996, they said.
He is also suffering from diabetes and hypertension.