Nawaz Sharif, leader of Pakistan's largest opposition party, is being treated at a London hospital for heart problems, a spokesman for his political party said Wednesday .
Sharif was admitted to a hospital Monday, but his condition is now stable and doctors are carrying out more tests, said Ahsan Iqbal, spokesman for the Pakistan Muslim League-N.
"He experienced some symptoms, some heaviness in his (chest), and the doctors asked him to come in," he said.
Family friend Mazar Ahmed said Sharif is "perfectly OK" and the hospitalization was part of a regularly scheduled check up. He added that the 61-year-old is due to be released Thursday.
Sharif served as Pakistan's prime minister for two nonconsecutive terms, during which he supported the Taliban regime in Afghanistan and tried to vastly increase his powers of his office while pushing aside Pakistan's penal code in favor of an Islamic justice system. Many saw these ill-fated moves as an attempt to "Talibanize" Pakistan, which eroded his popularity. He was overthrown in a 1999 coup by then-Gen. Pervez Musharraf.
As the leader of Pakistan's present opposition party, Sharif has walked a careful line, making it hard to ascertain if he is pro-Taliban or pro-United States.
His party _ a front-runner for the 2013 elections _ recently withdrew from a coalition government with President Asif Ali Zardari's Pakistan Peoples Party, of which Sharif has been a sharp critic. Zardari is the widower of former Prime Minister Benazir Bhutto, who was killed in a suicide bombing in late 2007.
In the past few weeks, tensions between the two parties have increased because of the arrest of a CIA contractor in the capital, Punjab, for shooting dead two Pakistanis. Both parties have accused the other of mishandling the aftermath of the arrest.
Paisley Dodds contributed to this story.