Eighty-nine-year-old Chatterjee, who is suffering from a kidney-related ailment, was admitted to the hospital on Tuesday.

"He is undergoing dialysis. In such cases it happens at times that the heart stops giving support. Chatterjee suffered a mild heart attack this morning, but was revived. He is in the ICCU and has been put on ventilation. He is responding to treatment," a senior hospital official told PTI.

Last month, the former speaker had suffered a haemorrhagic stroke.

"He has been under treatment for the past 40 days. Chatterjee was discharged from the hospital just for three days after his health showed signs of improvement. However, his condition deteriorated last Tuesday and he had to be hospitalised again," the official said.

A 10-time Lok Sabha MP, Chatterjee was a central committee member of the CPI(M), which he had joined in 1968.

He was the Speaker of the Lok Sabha from 2004 to 2009.

The veteran leader was, however, expelled from the CPI(M) in 2008 for refusing to resign as the Speaker after his party withdrew support to the UPA-I government.