Houston (AP) -  Ex-Polish President Lech Walesa may have to cancel planned meetings in Mexico if doctors decide to keep him under observation at U.S. hospital where he had a pacemaker installed, an aide said Monday.

Walesa, 64, was successfully fitted with a pacemaker on Friday at the Methodist DeBakey Heart and Vascular Center in Houston, Texas.

Doctors said Walesa is doing fine and expected to remain hospitalized until Wednesday for observation, his aide, Piotr Gulczynski told The Associated Press.

He said that if Walesa has to remain under doctors' care longer, the Nobel Peace Prize winner may have to postpone his planned meetings with youth in Morelia, Mexico, which are currently scheduled for Thursday through Saturday.

"In case the stay in hospital or under doctors' care is extended by a day or two ... we may have to change plans and arrive there at a different point in time," Gulczynski said. "Or there may be no reason to go there, after all, because the planned events may be over by then."

Gulczynski, who is flying to Houston to join Walesa on Tuesday, said a decision would be made after consulting with Walesa's doctors.

He added that Walesa was doing well and that any cancellations were not health-related.

Walesa was planning to return from Mexico to his Baltic hometown of Gdansk on Sunday.

Walesa, a former Gdansk shipyard electrician, led a workers' strike in 1980 that grew into the nationwide Solidarity freedom movement against Poland's communist authorities, earning him the Nobel Peace Prize in 1983.

In 1989, Solidarity toppled Poland's communist regime and Walesa served as the country's president from 1990-95.