Former Malaysian Prime Minister Mahathir Mohamad is in intensive care after being admitted to hospital with breathing difficulties, his aides say.
Mahathir Mohamad is an influential figure in Malaysia
The 81-year-old was said to be under observation at the hospital on the resort island of Langkawi.
Dr Mahathir, who has a history of heart trouble, suffered a mild heart attack last November.
Malaysia's longest serving prime minister, he spent 22 years in office before his retirement in 2003.
He still wields considerable influence on domestic politics and business.
"He was having breathing difficulty," Dr Mahathir's aide Sufi Yusoff was quoted by Reuters news agency as saying.
"They took him to Langkawi hospital at 1550 (0750 GMT). He is being held for observation at the intensive care unit."
The former prime minister is in a stable condition, according to the Star newspaper, which sent a text alert to mobile phones.
Dr Mahathir, a former medical doctor, suffered a mild heart attack last November after a visit to New Zealand. He underwent heart bypass surgery in 1989.
Langkawi - in Dr Mahathir's home state of Kedah - was playing host on Monday to a meeting between Prime Minister Abdullah Ahmad Badawi and his Singaporean counterpart Lee Hsien Loong.
Dr Mahathir has been critical of Prime Minister Badawi - his chosen successor - in recent years, accusing him of corruption, nepotism and mismanaging the economy.
Analysts believe he has been angered by changes introduced by Abdullah Badawi that appear to be partially dismantling his legacy.
While Dr Mahathir has a controversial reputation abroad for scathing comments about the West and scant regard for human rights, he is considered the father of modern Malaysia.
During his time in office, he helped transform Malaysia from a mainly rural economy into an Asian economic tiger.