"We have seen the reports. We certainly wish him a speedy recovery," said White House spokesman Jay Carney.
Zardari's illness sparked media reports that he is contemplating resignation, but loyalists ruled out the idea he may step down.
State Department spokesman Mark Toner, asked if the United States was worried that a quiet coup was underway against the embattled president, said: "No concerns and no reason to believe" the speculation.
"Our belief is that it's completely health-related," Toner told reporters.
Zardari is considered to have a fraught relationship with the military, which historically has been Pakistan's most powerful institution and has repeatedly pushed aside elected leaders.
Mustafa Khokhar, an adviser to Pakistan's prime minister on human rights who sits in the cabinet, told AFP in Islamabad that Zardari suffered "a minor heart attack" on Tuesday.
"He flew to Dubai where he had an angioplasty. He's in good health now," Khokhar said.
"There's no question of any resignation," he added.
The 56-year-old head of state left Pakistan for treatment after falling ill in the midst of a major scandal over alleged attempts by a close aide to seek US help to limit the power of Pakistan's military.
His illness also comes at a time of deep crisis for Washington's fraught anti-terror alliance with Pakistan.
Ties between the United States and Islamabad plummeted after a US commando raid killed Al-Qaeda leader Osama bin Laden in the Pakistani garrison town of Abbottabad, north of the capital Islamabad, in May.
Relations slid to a new low last month when Nato air strikes killed 24 Pakistani soldiers on the Afghan border, prompting Pakistan to boycott an international conference in Bonn on Afghanistan's future.
US President Barack Obama on Sunday expressed condolences to Zardari in a telephone conversation over the deaths but said the incident was not a "deliberate attack."
Pakistan president in Dubai with heart condition
Pakistan's embattled President Asif Ali Zardari will remain in hospital in Dubai until further notice after suffering a minor heart attack and undergoing an operation, officials said Wednesday.
The 56-year-old head of state flew to the United Arab Emirates on Tuesday after falling ill in the midst of a major scandal over alleged attempts by a close aide to seek US help to limit the power of Pakistan's military.
His illness sparked media reports that he is contemplating resignation, but loyalists have ruled out any question that he may step down and the president has defied many critics in already holding onto power for three years.
"He had a minor heart attack on Tuesday. He flew to Dubai where he had an angioplasty. He's in good health now," Mustafa Khokhar, adviser to the prime minister on human rights who sits in the cabinet, told AFP.
"There's no question of any resignation," he added.
The prime minister office said the president was "stable" but would remain under observation as doctors examine the cause of his illness.
A statement gave no timeframe for the treatment and made no mention of a heart attack, saying only that he went to Dubai following symptoms related to a "pre-existing heart condition" at the "insistence" of his three children.
Zardari is out of the country at a time when Pakistan is battling a major crisis in US relations after NATO air strikes killed 24 Pakistani soldiers on November 26.
In his absence, his powers are transferred to the chairman of the Senate, Farooq Naek, a senior member of Zardari's Pakistan People's Party (PPP).
One cabinet minister told a television show that he was being kept in intensive care, but only as a means of keeping visitors to a minimum.
"President Zardari's condition is now stable. He was taken to ICU because he was getting a lot of visitors," Petroleum Minister Asim Hussain told Geo TV.
"He will stay there for the next two to three days and will be back home after that."
The PPP spokesman Qamar Zaman Kaira told AFP that President Zardari has undergone different tests. "All the tests conducted so far are normal and he (Zardari) is stable."
He was however, not sure when the President will be back home. "It is difficult to say anything right now. It will depend on the doctors' advice."
Dubai's ruler, Sheikh Mohammad bin Rashed al-Maktoum, visited Zardari and wished him a "speedy recovery," the official WAM news agency reported.
Zardari took office after the PPP won general elections in February 2008, three months after his wife, former prime minister Benazir Bhutto was assassinated.
Although he has survived numerous crises and calls for his resignation, he has come under growing pressure over a memo allegedly written by close aide Husain Haqqani asking for American assistance in curbing the powerful military.
Haqqani was forced to resign as ambassador to Washington last month and Zardari said Sunday that he would soon address a joint session of parliament.
It was not clear if the health scare would delay that plan.
Presidential spokesman Farhatullah Babar dismissed reports that he may be forced to step down as "speculative, imaginary and untrue".
The United States also dismissed rumours of a coup against Zardari.
"Our belief is that it's completely health-related," said State Department spokesman Mark Toner.
But the website of the US magazine Foreign Policy reported that Zardari had been considering his resignation over health fears and the "Memogate scandal".
The article quoted an unnamed former US government official as saying Zardari was "incoherent" when he spoke to President Barack Obama by telephone over the weekend following the lethal NATO strikes.
The scandal centres on a memo sent in May to the US's then Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, seeking help over fears of a military coup following a secret US raid that killed Osama bin Laden on May 2.
Mansoor Ijaz, a Pakistani-American businessman, accused Haqqani of crafting the memo with Zardari's support. Haqqani has denied involvement and investigators have yet to prove to what extent Zardari may have been involved.
Relations between the military and Zardari are understood to be tense. Haqqani's departure was seen as forced by the army and the political pressure on Zardari is mounting ahead of elections expected as early as next autumn.
In June, US pollsters Pew Research Center gave Zardari an approval rating in Pakistan of only 11 percent.
COMMENTS (20)
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ
In words of a renowned jounalist "It seems that humanity has taken leave of this country and there is no respect for human life. President Zardari is a democratically elected president; neither is he someone who came to power via the backdoor nor is he a military dictator. Dragging down the dignity of the office of the president just because some people do not like the individual at the helm of affairs is rather unfortunate."
I guess the USA providing Zardari good wishes is almost as bad as them giving money to Pakistan -- seems to really irritate the anti USA crowd.
@antanu: Absolutely right u r.
what business does Obama has in the internal matters of Pak?
Who the hell America is to confirm or dismiss the rumours.
Musharraf is good. But Imran Khan it is time you step up!
The question is, who will replace Zardari if he'd step down? Pervez Musharraf is eager to return to office. Do you want him back?
Not sure why US thinks that statement is required or is necessary to come from them.
Most of the comments are in bad taste...as a politician Zardari may be good or bad, based on one's perception...but as a human being ridiculing his illness is not humane. We claim to be civilized and feel it our birth rights to start hating wrongdoers (even if we ourselves are a cheater in our daily lives) but our scant respect for human suffering reflects a mindset not worthy of humanity.In a way we are just like Talibans...they are violent physically and we are mentally.
May God keep president safe.
Get well soon Mr. President.
@Omar: The personal medical record is the patient's own and cannot be shared with anybody even another doctor without his/her permission. The doctors can be fired and their license taken away if they are found to break their medical oath and ethics. This is what is supposed to happen but one can never be sure about Pakistan. Regards, Mirza
I wish him speedy recovery. Not that i care but I don't want another PPP political shaheed.
US always play against the wishes of Pakistani ppl
They have seen his medical reports. I want to see them too. Not that I'm a docgtor but if they can have access, why should I be left out?
"The reports of my death are greatly exaggerated" Origin: Mark Twain quotation after hearing that his obituary had been published in the New York Journal.
DOnt shatter our hopes mr Obama :(
Thank you U.S. for clearing the confusion. Now go run your own country.
Wishful thinking turning in to news. Not a good time to lose president. wish him get well soon
This is how wishful thinking of people turn into news.