The spokesperson said Mahathir was admitted to the cardiac care unit at the National Heart Institute but gave no details.
This is the second time the 96-year-old, who is still an active lawmaker, has been admitted to the hospital this month. He was discharged after what was described as an successful elective medical procedure last week.
The National Heart Institute did not say at the time what procedure Mahathir, who has a history of heart problems, had undergone.
He was admitted and discharged in December after his doctors said they were satisfied with the results of necessary investigations.
Mahathir was prime minister from 1981 to 2003 and held the top post again from 2018 to 2020.
