Dr Mahathir had been suffering from fever and cough prior to his admission.
Tun Dr Mahathir Mohamad was hospitalised today with a suspected chest infection, following a recent fever and coughing bouts.
The former premier was admitted at the National Heart Institute (IJN) early this morning, and is currently undergoing antiviral treatment and physiotherapy for his chest condition.
Dr Mahathir has been told not take visitors unnecessarily at the hospital, where doctors expect to keep him until the end of the week.
The 85-year-old former prime minister has a history of heart complications and underwent two heart operations — once in 1989 and another in 2007.
The second, a heart bypass operation, was also conducted by surgeons at IJN.
In October of last year, Dr Mahathir was hospitalised during a trip to Melbourne, Australia, where he was admitted to Epworth Hospital there for three days after suffering from flu and cough.