Crowds thronged the hospital on Sunday evening while top leaders and common people across India prayed for her well-being and recovery.
"Our doctors are closely monitoring Hon'ble CM's condition and they are trying their very best," tweeted Apollo Hospitals Joint Managing Director Sangita Reddy on Monday.
Maharashtra Governor C. Vidyasagar Rao, who has additional charge of the state, returned from Mumbai and visited the hospital to enquire about Jayalalithaa's condition on Sunday night.
However he has not issued any statement after his hospital visit.
In the earlier occasion Raj Bhavan had issued a statement soon after he visited Apollo Hospitals.
On Sunday night the hospital said, in a statement: "The Hon'ble Chief Minister of Tamil Nadu who is undergoing treatment at Apollo Hospitals, Greams Road, Chennai, suffered a cardiac arrest this evening. She is being treated and monitored by a team of experts including cardiologists, pulmonologist and the critical care specialists."
It later said in a tweet that she "is on extracorporeal membrane heart assist device and is being treated by a team of expert doctors and critical care specialists".
"Dr Richard Beale from London has also been consulted and he has concurred with the line of treatment by our cardiologists & pulmonologists," it said in another tweet.
In an another tweet, the hospital said: "The Hon'ble CM is the beloved leader of the masses. Please join us in praying for her speedy recovery. #GodblessAmma #Jayalalithaa."
"The Apollo TN CM #Jayalalita is critical.multi speciality team @hospitalsapollo trying everything including ecmo.praying for her recovery," tweeted Sangita Reddy earlier.
While a large police contingent was deployed at the hospital, reports said that security was being stepped up across the state.
State ministers, senior officials and others gathered at the hospital, as did a huge crowd of AIADMK cadre, many of whom broke down while others fervently prayed for her recovery. Some tried to enter the hospital premises but were restrained.
Meanwhile according to reports some areas experienced shortage of milk supplies and traders jacked up the prices several folds.