"It's still a work in progress," he said. "But I'm have fun working at it."
Heyward is hitting .264 after a 2-for-6 performance in the 3-hour, 56-minute contest. He ripped a 1-0 pitch off reliever Kyle McClellan into the bullpen in left-center for the game's decisive runs.
"That was big-time," manager Fredi Gonzalez said. "We were running out of players, running out of pitchers in that situation. That's a big at-bat."
McClellan felt he got too much of the plate on the offering.
"I was trying to go down and away and get a ground ball," he said. "It was up more than I wanted it to be."
Heyward's fifth homer of the season ended a wild seesaw game that saw the Braves use their entire seven-pitcher bullpen. Closer Craig Kimbrel recorded his 11th save in 12 chances with a scoreless 12th. He struck out two batters and has recorded 17 of his last 24 outs via the K.
Atlanta starter-turned-reliever Livan Hernandez picked up the win with two scoreless innings. The veteran right-hander got pinch-hitter David Freese to ground into a bases-loaded double play to end a threat in the 10th. Hernandez picked up his career first relief win in his 12th appearance out of the 'pen after 474 starts. He also recorded a save with 1 2/3 innings of scoreless relief in a 13-9 triumph at Colorado on Saturday.
All of a sudden, the 37-year-old is enjoying his newfound relief role.
"I'm relaxing and trying to do my best," he said. "It's different -- but I've started to like it."
Hernandez also got Allen Craig to pop out with the sacks jammed to end the 11th.
"I think the experience of Livan pitching all those games helped into those situations where he never gave in," Gonzalez said. "He's got the command and he knows where the ball is going."
The Braves, who moved to 3-0 in extra-inning games, improved to 5-2 on their current nine-game road trip, which began with a three-game sweep in Colorado.
Atlanta had lost its previous seven games in St. Louis and had been outscored 39-20 heading into Friday's contest.
The come-from-behind triumph provided a shot in the arm for the Braves, who won in St. Louis for the first time since a 9-2 win on Sept. 13, 2009.
"That happens sometimes," Heyward said. "They've had a good team here for years now, they've got a good team here now. We battled back and hung in there."
The Braves, who have won 20 of their last 29 games, received several clutch performances down the stretch. Freddie Freeman gave Atlanta a temporary 7-6 lead with a two-out RBI infield single in the eighth, before St. Louis outfielder Carlos Beltran responded with his second homer of the game to tie it 7-7 in the bottom of the frame. Beltran had four hits and four RBIs.
Michael Bourn, who had a 12-game hitting streak snapped Wednesday in Chicago, went 3-for-6 and singled in each of the first two innings to help stake starting pitcher Mike Minor to leads of 2-0 and 5-1. Bourn has a hit in 24 of 27 games since April 13. He recorded his team-high 13th multihit game and sixth three-hit game of the season Friday.
But Minor gave up six earned runs and lasted just 4 2/3 innings. The left-hander was coming off a pair of rough outings, the first of which he surrendered a career-high seven runs in a 9-3 loss to Pittsburgh on April 30, before following that up by allowing eight runs to Colorado on Saturday. Minor, who is 0-1 with an 11.81 ERA in last three starts, gave up eight hits and six runs while striking out seven.
"I felt good early on," he said. "They're a good hitting team, and they did what they are supposed to and hit some home runs off me."
Atlanta used RBI hits by Brian McCann and Chipper Jones and a two-out double by Taylor Pastornicky off St. Louis starter Jaime Garcia to a take 5-1 lead in the top of the fourth.
But the Cardinals fought back with three in the bottom of the fifth. Minor gave up singles to Rafael Furcal and Jon Jay before Matt Holliday cut the deficit to 5-4 with a double. Beltran then slammed a two-run triple to dead center to give St. Louis its first lead of the night at 6-5.
Dan Uggla brought the Braves back from a 6-5 deficit with a game-tying homer in the seventh. It was his fifth of the season.
Jones had two hits and scored twice in what could be his last series in St. Louis. He was given a 45-second standing ovation by the crowd in his first trip to the plate.
Matt Carpenter and Allen Craig also homered for St. Louis. Minor gave up a season-high three round-trippers.
It was the longest game of the season for the Braves.