Premier Danny Williams is at an undisclosed location in the U.S. preparing to have heart surgery. (Jeff McIntosh/Canadian Press)

Newfoundland and Labrador Premier Danny Williams will be sidelined from three to 12 weeks because of heart surgery he'll undergo at an undisclosed location in the United States, acting premier Kathy Dunderdale says.

Williams, 60, travelled to the U.S. on Monday on the advice of his doctors after weeks of consultations, Dunderdale said.

"I'm not going into the details of the premier's condition," she told reporters at a news conference in St. John's on Tuesday morning. "Any heart surgery is serious. However, his prognosis is very, very good."

Dunderdale said the surgery would happen this week but refused to provide specifics on the day or where Williams is being treated, other than to say he has "gone to a renowned expert in the procedure that he needs to have done."

She also wouldn't say whether Williams could have had the procedure performed in the province or elsewhere in Canada.

"Having the surgery done in the province was never an option that was offered to him," Dunderdale said.

"Ultimately, we have to be the gatekeepers of our own health, and he has taken medical advice from a number of different sources," she said. "Based on all of the medical advice that he's received, he is doing what is best for him, to do everything he can to ensure that he can have the best outcome from the surgery and that he can be back on his feet and back here doing his job as quickly as possible."

Dunderdale said Williams will speak about the procedure and his decision to go to the U.S. for treatment when he recovers.

"The premier has made a commitment that once he is through this procedure and he is well enough, he's going to talk about the whole process and share as much detail as he's comfortable doing at that time."

The CEO of Eastern Health, the province's largest health authority, tried to dispel any notion that Williams left the province because of a lack of faith in the province's — or Canada's — health-care system.

"There's no question that this is not a queue-jumping issue," Vickie Kaminski told reporters.

She said patient confidentiality restricts her from discussing the specifics of Williams' heart condition or the kind of medical procedure he will undergo. However, she confirmed the premier had all of his diagnostic work and tests done at Eastern Health.

"He certainly has told us that he was very satisfied with the care that he received," she said.

Kaminski said it was his doctors who suggested Williams leave the province for treatment.

"The recommendations from his physician were for referrals outside. The premier has done what he was recommended."

Kaminski said people shouldn't view his decision to seek medical help elsewhere as a condemnation of Canada's medical health system.

"It could be something as simple as a slightly new technique that's being tried that gives a speedy recovery and that's not yet approved in Canada," she said.

Kaminski said it might also be a procedure that can't be performed for whatever reason by medical professionals in the province.

Doctors in Newfoundland and Labrador refer two patients a month to physicians outside the province, depending on the medical condition. Kaminski said about 50 people are on a waiting list for heart surgery — down dramatically from two years ago — and the amount of time those people have to wait is medically acceptable.

Dunderdale will be acting premier until Williams returns to the job.