The Braves said Heyward's jaw has been stabilized, and he was to return to Atlanta on Wednesday night in advance of the operation. How much time Heyward will be sidelined is expected to be announced after the operation, but MLB.com estimated he would be out for 4-6 weeks.
Heyward was beaned by a 90 mph fastball from New York Mets left-hander Jonathon Niese in the sixth inning of the Braves' 4-1, 10-inning win on Wednesday. The impact made a loud noise, and the crowd groaned as Heyward crumpled to the ground.
He stayed down on his back for about three minutes before getting helped to his feet. Heyward walked slowly off the field under his own power, escorted by a trainer, and was replaced by Jordan Schafer.
Heyward's grandparents were at Citi Field and accompanied him to the hospital, along with trainer Jeff Porter. Heyward and Porter stayed behind in New York as the Braves traveled to St. Louis for a four-game series that begins Thursday night.
"He never lost consciousness," manager Fredi Gonzalez said. "Right before he went to the hospital he popped his head into the clubhouse to say goodbye to some of the guys.
"It's not the ballpark, it's just a matter of freak stuff happening. It can happen anywhere."
Visibly concerned, Niese tapped himself with his glove as Heyward walked off, and Heyward appeared to acknowledge him.
"I felt horrible," Niese said. "Sometimes this game can be pretty dangerous. One minute you're playing, the next you're down. I felt terrible."
An inning later, the Mets announced that Heyward was examined by their doctors before he was taken to the hospital for further examination.
"Scary, to be honest," Mets catcher John Buck said. "You don't ever want to hit anyone in the head. Saw him spitting up blood; that was even scarier."
Simmons and Freeman were among several Braves players who took to Twitter to express their concern and send best wishes Heyward's way.
— Andrelton Simmons (@Andrelton) August 21, 2013
Please pray for my dude @JasonHeyward ! Hoping for good news! ��
— Freddie Freeman (@FreddieFreeman5) August 21, 2013
On a tear at the plate since moving into the leadoff spot last month, Heyward began the day batting .254 with 13 homers and 37 RBIs on the season. Atlanta entered Wednesday with a 15-game lead in the NL East.
Information from The Associated Press and ESPNNewYork's Matt Ehalt contributed to this report.