The National Heart Institute of Malaysia said in a statement, according to Reuters.
Mahathir Mohamad, 96, a former prime minister, needs full medical treatment and checkups and more supervision.
The reason for the former Malaysian prime minister being hospitalized has not yet been determined, and his spokesman has declined to comment.
Mahathir Mohamad is expected to remain in hospital for the next few days.
Mahathir, Malaysia's longest-serving prime minister, served 22 years until 2003. He has a history of heart disease and has had heart attacks and heart surgery before.
He returned to the presidency at the age of 92 after leading an opposition coalition with a historic victory in 2018 and the defeat of the party he once led. His government collapsed in less than two years due to civil strife.
Mahathir Mohamad is still an influential figure in Malaysian politics.