Boone completed a minor league rehab assignment and will be activated when major league rosters expand on Sept. 1.
"Everything's gone well," Boone said before the Astros met the Arizona Diamondbacks on Friday night. "To see yourself improve every day, every week, every month, has been satisfying."
The 36-year-old Boone signed with the Astros in the offseason, then had an operation in late March because of a congenital defect in his aortic valve.
Boone's role with the Astros is unclear; he may see only occasional at-bats in September.
Asked what is the biggest hurdle he's facing on the field, Boone replied, "Just getting to that elite. You realize how tough it is to play this game at a really high level, and just to get all the way back there, it's a fine line."
Boone said he had long known that surgery was a possibility with his condition, and he didn't think about the possibility that his career might be over when doctors told him during spring training that he would need an operation.
"Initially, I didn't care," Boone said. "Once I was OK, my whole thing was, I was going to try and get myself in shape, and whatever that led to, great. I love this game. I'm not addicted to it, and if it was over, that would have been OK, too."
A member of one of baseball's most famous families, Boone is best known for hitting a pennant-winning homer for the New York Yankees in the 11th inning of Game 7 of the 2003 AL Championship Series.
The son of former big league catcher Bob Boone, Aaron Boone is also grandson of infielder Ray Boone. Aaron's brother, Bret, played 14 seasons in the major leagues, too.
If Aaron Boone plays this year, it would be his 12th season in the majors.
He has played for Cincinnati, the Yankees, Cleveland, Florida and Washington, batting .264 with 126 homers and 555 RBIs. Boone was a member of the 2003 NL All-Star team as a Red.
"I've had an awesome career," Boone said. "I've had a lot of ups, a lot of downs, a lot of injuries, a lot of comebacks. The career I've had, I feel so blessed to have had it, and I certainly appreciate it and am grateful for it."
Boone said he doesn't consider himself a role model for others who have undergone open-heart surgery, but he knows that many are watching his comeback.
"As far as a role model, I always find that odd that I could be that, but I've realized that it at least has touched people with maybe something similar," Boone said. "Certainly, I think that's in the equation as part of my wanting to do this. I don't know if it's an obligation. That might be a little strong. But it's in the equation of reasons to be back."