The team said late Monday that Heyward had surgery at Rose Medical Center in Denver.
Manager Fredi Gonzalez said before the opener of Tuesday's day-night doubleheader against Colorado that there was no set timetable for Heyward's return. The Braves recalled infielder Tyler Pastornicky from Triple A Gwinnett to fill Heyward's roster spot.
Heyward was off to a slow start, batting .121 with two homers and five RBIs. Still, the Braves began the day with a 13-5 record.
"A couple of days ago when we were in Pittsburgh, he felt like he had some stomach fires going," Gonzalez said, "and then it just kept getting more localized, moving to his right side."
After Monday night's game was postponed due to snow and the Braves returned to their hotel in Denver, Heyward called team trainers and said pain in his right side had become acute.
Team physician Dr. Joe Chandler examined Heyward, and tests revealed the problem with his appendix. Chandler accompanied Heyward to the hospital, with the Rockies medical staff helping smooth the admission process.
"Everything went well," Gonzalez said. "Dr. Chandler was here and he did a terrific job. The doctors from the Rockies helped out and got him into the hospital here. They got him in and got him out (of surgery) in about 45 minutes."
Gonzalez said he had a chance to visit with Heyward in the hospital before coming to the ballpark.
"He was in good spirits, beat up a little bit, as you can expect, from the surgery," Gonzalez said. "He's just drained."
Left fielder Justin Upton has played right field in the past.
"Justin is doing a great job in left field and why would I want to move him back for 10-12 days? He's getting used to that left-field position, so we'll just leave him there," Gonzalez said.
Gonzalez said Heyward may be discharged from the hospital as soon as Tuesday night but may remain in Denver for a day or two before flying back to Atlanta. Heyward won't be going with the team when it leaves after Wednesday's game for Detroit.