Close associates of the president told the Associated Press he is currently "unwell," but did not provide specifics. His condition did not appear to be life-threatening, they said, speaking on condition of anonymity because of the sensitivity of the issue.
Zardari's office said he was undergoing routine medical tests and a check-up "as planned."
However, Reuters cited a source in Dubai as saying that Zardari had suffered a minor heart attack.
"Two days ago, he had chest pain," the source added.Slideshow: Pakistan: A nation in turmoil
Prime Minister Yusuf Raza Gilani's office released a statement saying Zardari "went to Dubai following symptoms related to his pre-existing heart condition."