Former TERI chief R K Pachauri, who was admitted to the Escorts Heart Institute in the national capital with a prolonged cardiac ailment, was put on life support on Tuesday, sources said.
Pachauri, 79, underwent open-heart surgery at the hospital, they said.
The environmentalist had suffered a heart stroke in Mexico in July last year, said a source close to him, adding that he was critical and put on a ventilator.
"He was suffering from cardiac issues. He had open-heart surgery but was put on ventilator," the sources said.
Pachauri had to step down from his position in The Energy and Resources Institute (TERI) after he was accused of sexually harassing a former woman colleague.
A district court had in October 2018 framed molestation charges against Pachauri, who had repeatedly denied the allegations levelled against him.
During the court hearings, Pachauri had sought a speedy trial saying he and his family were suffering from hardship since 2015 when an FIR was lodged in the matter.
After the FIR was registered in February 2015, Pachauri was given anticipatory bail the next month.