In October last year, Karthikeyan sought expert treatment at the US-based Mayo Clinic and after a week he returned and was getting better here. He did not take part in the assembly session held in December.
Karthikeyan was present at the opening ceremony of the National Games held at the Green filed stadium, Thiruvananthapuram on January 31, but fell ill again after a few days.
Some Kerala ministers have already met the ailing speaker at the hospital here and sources said former defence minister A.K. Antony broke down on hearing the condition of his former colleague.
The mild mannered veteran Congress leader who hails from the capital district has been in politics from his student days and is a six time legislator. He was a cabinet minister twice.