Last May, Stacy Keach experienced every stage actor’s worst nightmare: He forgot his lines. During the opening night performance of Jim McGrath’s one-man play Pamplona at the Goodman Theatre, Keach stood in front of a confused audience and repeated the same line over and over. What Keach soon discovered, however, is that forgetting your lines isn’t the worst thing that can happen onstage. The next morning, doctors told him he’d had a heart attack. That was the end of the run, but it won’t be the end of Keach’s performance. In July, the Goodman will remount Pamplona, helmed by the theater’s artistic director, Robert Falls, with Keach once again taking on Ernest Hemingway. Keach, 77, spoke to Chicago about picking up where he left off.

Can you describe what happened last year?

About five minutes into the play, it felt like a fog rolled in over my brain cells. I didn’t have any kind of pain in my chest, but I had no idea what my next line was. After I repeated the same line more than half a dozen times, it became very apparent that something was wrong. So Robert Falls came onstage and ushered me off and told the audience the play was over. My wife, Malgosia, was in tears, and my daughter was in shock. I wanted to go back onstage, but the audience had left.

Did you go to the hospital right away?

They wanted to take me to the emergency room, but I was in no pain, and I was very cogent at that point. I said, “No, I’ll go to the doctor first thing in the morning.” The next day, I had a battery of tests, and I discovered I’d had a mild heart attack. I had some serious blockage in my arteries. And unless I underwent surgery immediately, there was a good chance the same condition would reoccur. So I had a triple bypass at Northwestern.

Pamplona will mark your first stage appearance since then, but you have already started working?

I spent six weeks recovering in Chicago, but I got back to work two weeks after the surgery—I did voice-over work. And in August I started the CBS series Man with a Plan, playing Matt LeBlanc’s dad.

Do you have any fears about returning?

None whatsoever, just anticipation and excitement.

Starring in a one-man play six days a week for six weeks—that’s a big undertaking. How have you gotten ready?

It’s a tremendous challenge. The most important thing for me is to be in good enough physical shape. So I watch my diet and I exercise; I swim in the pool every day. I feel terrific. My doctors are telling me—I’m knocking on wood as I’m saying it—that I’m in the best shape of my life. The heart attack actually ended up saving my life.