Bhattacharjee, admitted to the Intensive Care Unit of privately-run Woodlands Hospital here on Friday night with breathlessness and low blood pressure, was administered a unit of blood.
"He is under intensive monitoring. He is now stable. His blood pressure has stabilised. He has a chest infection and is on antibiotic," a hospital official said.
Bhattacharjee's condition has improved since his admission, the official said.
State Governor Jagdeep Dhankar and Chief Minister Mamata Banerjee visited Bhattacharjee on Friday night itself.
Dhankar, who spent about 15 minutes with Bhattacharjee at the hospital, said: "He spoke to me and thanked me. Doctors are taking very good care of him."
The 75-year-old leader has been suffering from progressive lung problem, chronic obstructive pulmonary disease (COPD), for years. He was being treated at his Palm Avenue residence for long, but hospitalisation became necessary as his condition deteriorated and blood pressure fell.
A seven-member medical team has been formed for Bhattacharjee's treatment.
"No rumours. He is fine. His condition is stable," Communist Party of India-Marxist (CPI-M) politburo member Mohammad Salim told mediapersons at the hospital on Friday night.
Bhattacharjee, who was the Bengal Chief Minister during 2000-2011, undertook an all-out industrialisation drive for reducing unemployment in the state but the measure proved counter-productive.
Bhattacharjee was seen last in public on February 3, when he went to the Brigade Parade ground to attend a rally called by the Left Front.
( With inputs from IANS )