"This is the first step to being ready to start pitching," Garza said Thursday. "I'm not going to rush this thing."
He threw for about 15 minutes and called the session "baby steps."
"It was good to be out there, good to throw, and now it's just back to re-evaluation and see where we're at again and go from there," Garza said after his workout.
"My target's just to get healthy. I'm not putting a timeframe on it, just because when you do that, you're either too short or too long. So I'm just going to where I'm healthy and when that happens, then I'll be right back in the mix."
Garza admitted to being a little anxious.
"It was nerve-wracking, but after I got done, it was like a sigh of relief," he said. "Eleven days inside stinks. But you know it's progress, and I've been making a lot of progression, so I'm pretty pumped."
Garza missed the last 2 1/2 months of the 2012 season because of a right elbow problem, but he had thrown at least six bullpen sessions before he was injured. The good news is the arm feels great. Garza, Jeff Samardzija and Edwin Jackson were contenders for the Opening Day assignment, but Garza now needs more time.
"The schedule isn't for Opening Day or opening week," Garza said. "The schedule is for when my body is ready."
He's not going to push it.
"If I try to rush and be ready April 1, I might be reinjured in June and be out," Garza said. "If I take my time, maybe I'm pitching April 15 through October, maybe November."
Cubs manager Dale Sveum did not want to put a timetable on Garza.
"It's way too early to evaluate," Sveum said. "We have to evaluate today before we evaluate or even think that far down the road. If everything goes good today, we're planning on him being ready for the start of the season."
Garza's next throwing session will most likely be Saturday as he continues to build up his arm. The soreness in his side has only limited him when he turns his body.
"I think my arm strength will be there," Garza said. "I think it'll be more conditioning, just up and down, up and down, and teaching myself back my mechanics. I haven't been able to do that for 10 days, so there will be some rustiness there. Arm strength won't be an issue."
All the Cubs want to hear is that there are no problems with the elbow.
"There's no concern there -- it's just caution," Garza said of his arm. "I'm just going to take my time and be easy with it and make sure it's nice and free flowing. If there's any snag, then speak up. This is a time where a guy like me, I love being out there. I've got to swallow my pride and put the team first."
"If there was a setback because of the elbow, we would've had some issues," Sveum said. "There was obviously a very slight rib-cage thing. That's what we were worried about when he first did it -- 'OK, here we go, four-to-six-week thing.' It was basically as minor as you could get."
Garza, who said he felt like a caged animal during his offseason rehab, was very eager to throw, even if it was just playing catch.
"It's more anxiety -- I feel left behind," he said. "I'm not out there. That's what sucks. Injuries happen, and if I speed it up, it could happen again. I'd rather take my time with it and champ at the bit a little longer than having to champ at the bit for six weeks instead of 10 to 12 days."
Garza had six bullpen sessions before the live BP session that he cut short after 20 pitches.
"It's kind of like I took a two-week vacation," he said of the time off. "I haven't had one, so maybe that's why it happened."