She was taken to Mercy Medical Center-North Iowa by ambulance from the airport.
"As a precaution, Mrs. Heinz Kerry had a series of routine tests performed and was released," said Sarah Gegenheimer, a spokeswoman for Heinz Kerry. "She is feeling better and is traveling to her home in Pittsburgh tonight as planned."
Heinz Kerry had just finished a private meeting with a group of local Democrats to talk about health care.
"She was just fatigued I think. She said she felt a little dizzy at one point," said Steve Musson, a local restaurateur at whose home the gathering was held.
"She was only here a couple hours," Musson said. "She had a glass of water and didn't eat anything. ... She seemed fine when she left here."
Kerry had been campaigning separately in Ohio when his wife became ill. He drove in a motorcade to their Pittsburgh home early in the evening.
Heinz Kerry was visiting her fourth Iowa city in two days. She had earlier stopped in Cedar Rapids, Davenport and Des Moines, talking about rising health care costs and shrinking coverage.
Two of her stops were in private homes.
Musson, who said he had met Heinz Kerry twice before, said he was asked to keep the meeting a secret.
"It was a group of local people. ... She wanted to know about people's concerns and talked for 20 minutes about John Kerry's health care policies, heard peoples' stories, responded to that and offered advice," he said.
"She did seem very tired," he said. "She has done a lot of events in a short period of time."
The episode with Heinz Kerry came one day after the disclosure that former President Clinton, who had been expected to campaign for the Kerry ticket, was in the hospital about to undergo.