"It was great to get back out there and be a part of a real game," Boone said. "It didn't go our way, but it was certainly good to get out there and get the competitive juices going and deal with your nerves. I felt pretty good."
Boone flied out to left field in the second and fifth innings and grounded out to shortstop in the eighth. He played all nine innings and was on deck when the game ended.
"It was a good day for him to get out there," Astros manager Cecil Cooper said. "I'm glad he got a chance to do it. I wish we could have gotten better results. It wasn't to be, but I'm glad for him that he got a chance to play."
The significance of the moment certainly wasn't lost on the Cubs.
"Even going over it in our pregame plan, we knew he was hitting [seventh] and Teddy [Lilly] and I both mentioned, 'Good for him,'" catcher Koyie Hill said. "It's a great story. I told him I was happy for him and glad he was back doing what he loves to do."
Boone, 36, is believed to be the first player to return to the Major Leagues following open-heart surgery. He underwent surgery March 26 at Stanford University Medical Center to repair a valve in his heart that threatened the aorta.
"I was a little nervous being in the field," Boone said. "I was fine last night and all today, and running out there I was a little nervous. I got into the flow of the game pretty quick. At first, you handle the ball a lot and it kind of gets you into it, and once you get going, it felt pretty good."
Astros first baseman Lance Berkman, who was out of the starting lineup Wednesday to make room for Boone, said he never thought Boone would play again when he told his teammates during an emotional news conference March 18 he would undergo the surgery.
"I thought he was done permanently, not just this year," Berkman said. "It's a testament to him wanting to come back. It's great that he's going to get an opportunity to play, and everybody across baseball is happy to see him out there."
Boone lost 15 pounds following the procedure, but by June was beginning light workouts at Minute Maid Park and regaining his strength. He had progressed enough by late July to begin taking batting practice and started discussing a possible return with team officials.
On Aug. 10, Boone began a Minor League rehab assignment, during which he played in 11 games combined between Triple-A Round Rock and Double-A Corpus Christi. He rejoined the Astros on Friday in Arizona, where he lives, and was activated on Tuesday.
Boone was tested in the second inning Wednesday when Cubs third baseman Jeff Baker hit a sharp ground ball down the first-base line. Boone knocked the ball down as he fell on his chest and recovered in time to throw to pitcher Felipe Paulino covering first base for the out.
"I didn't have time to think about it, so it worked out," Boone said. "It was good to get thrown right in the fire and get some action. All in all, it was just really good to be out there, really rewarding."
A career .264 hitter with 126 homers and 555 RBIs in 11 seasons, Boone is relieved to have resumed his career. He's keeping the door open about playing next season, but for now he's not willing to look past Friday night's game against Philadelphia.
If he's learned anything, it's to enjoy each moment.
"I just want to be healthy and contribute to some wins and enjoy these guys," Boone said.