Regis Philbin may still be recuperating from his heart bypass surgery six weeks ago, but he did not miss a step —or a joke—on his first day back at “Live With Regis and Kelly” Thursday morning, which also was the first day of the May sweeps ratings period.

“I don’t feel that great,” he told a White House-sized press corps assembled after the broadcast, pointing to the chest that was cracked open and to the upper leg from which veins were taken to bypass those that had clogged around his heart.

“I wasn’t itching to get back,” he said. “But it was time.”

It was a good time Thursday that starting with his New York City studio audience chanting “Regis. Regis. Regis” as the tanned and trim Mr. Philbin and co-host Kelly Ripa took their assigned seats together for the first time since he announced he would have the surgery.

CBS “Late Show” host David Letterman, himself a veteran of a 2000 bypass performed by Mr. Philbin’s surgeons, made a rare appearance outside his own studio to share the stage with Mr. Philbin and Ms. Ripa for much of the hour, which was both light-hearted and enlightening.

“If you’re a hypochondriac, this is right up you’re alley,” said Mr. Letterman, who arrived bearing one of the T-shirts—complete with a row of red “stitches” down the front—with which he had commemorated his own surgery.

“Don’t be a hero,” Mr. Letterman said, jokingly advising Mr. Philbin to lie down if he felt the need and to “stay away from ‘The View'” if he wanted to avoid unnecessary stress. That was, of course, an allusion to the season of tumultuous feuds and headlines that will presumably, end in June with the exit of Rosie O’Donnell from the ABC daytime show.

Mr. Philbin and Mr. Letterman compared anesthesia and recovery stories and leg scars and welcomed the surgical team that repaired Mr. Philbin’s heart.

After the show ended with an energetic performance five dancers billed as the “Dancing Regi” and a heart-healthy pink and white cake, Mr. Philbin told reporters from as far away as WSVN-TV in Miami, he’s been walking every day, doing a lot of reading and “laying low” with wife Joy, who will appear Friday to talk about the last six weeks from her perspective.

Mr. Philbin said it was an unusually long stretch in which they were together 24/7 and “I loved it.”

He said the get-well gifts he had received included bathrobes from Madonna and Halle Berry and a basket of green apples from Ringo Starr.

Asked about supermarket tabloid rumors that he and/or wife Joy planned for him to cut back his work load so he can slow down and smell the roses, Mr. Philbin made clear he is neither retiring nor shirking.

“Live,” he said, “Is part of my life.”