Kuala Lumpur
The 96-year-old is being treated at the National Heart Institute's cardiac care unit, the spokesman said in a brief statement.
Prior to this, Mahathir was admitted to the National Heart Institute for a full medical check-up and observation on December 16-23 last year, reports Xinhua news agency.
He was admitted to the same hospital for an elective procedure on January 7 and was discharged on January 13.
Mahathir had served as Prime Minister for two terms: the first between 1981 and 2003 and the second from 2018 to 2020.
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