It took eight years, but Noah Wyle is on the verge of becoming ER's new chief of staff. With Anthony Edwards checking out on May 9, Wyle soon will be the show's longest-running cast member.

"I've been very curious to see what it will be like to carry the show the way Tony's been carrying it for [eight] years," the 30-year-old tells TV Guide Online. "To find myself having incrementally climbed up the call sheet and now arriving at the number-one spot... I'm very excited at the challenge of being at the center of the ensemble that I've given a third of my life to."

Contractually, Wyle is committed to ER for two more years — through the show's tenth season. After that, he'll most likely look to be discharged. "There's something nice about ten years in my head. It's a nice round number," he says. "I think at that point I may be looking to leave the nest. But I'm not ruling anything out at the moment."

Unlike his dearly departed co-stars, Wyle admits emergency room duty isn't making him restless. "[The producers] have given me opportunities to do other jobs during the course of the shooting season and they've been incredibly supportive of all my endeavors," says the actor, who stars in the new J.Lo thriller Enough (opening May 24). "Until I want a lifestyle change the way Eriq La Salle wanted to become a director, and the way Tony wanted to move to New York and the way George [Clooney] wanted to solely focus on features, I have no real reason to leave.

"Except for the frustration that comes up every now and again about a movie that I'm just not available to do," he adds, "I really have very few complaints."

And why should he? Wyle's big ER promotion coincides with another major milestone: He and wife Tracy are expecting their first child. "[It was] much prayed for and much wanted," he says of the upcoming addition, whose gender will remain a mystery until his or her birthday. "We want to be surprised. We figure there are too few surprises left in this world."