With the score level at 1-1 in the 65th minute, Lockyer suddenly fell to the turf in a worrying scene.
Play was paused as the Luton defender received treatment from medics while both sides were sent to the dressing room.
Lockyer was eventually stretchered off, surrounded by the medical team, and taken immediately to hospital.
There was a standing ovation from the crowd, with fans in the Vitality Stadium chanting Lockyer's name.
"Our medical staff have confirmed that Tom Lockyer suffered cardiac arrest on the pitch, but was responsive by the time he was taken off on the stretcher," Luton said in a statement.
"He received further treatment inside the stadium, for which we once again thank the medical teams from both sides.
"Tom was transferred to hospital, where we can reassure supporters that he is stable and currently undergoing further tests with his family at his bedside.
"We would like to thank everyone for their support, concern and loving messages for Locks."
Around half an hour after the incident, referee Simon Hooper confirmed the game would not restart on Saturday.
Players from both sides returned to the pitch and applauded the crowd.
Lockyer also collapsed during Luton's Championship play-off final win against Coventry at Wembley in May.
The Wales international was taken to hospital and later underwent heart surgery.
The 29-year-old had an operation to correct an atrial fibrillation, a condition the UK's National Health Service (NHS) describes as causing "an irregular and often abnormally fast heart rate".
Lockyer returned to action for the start of Luton's first season in the top flight for 31 years.
He had made 15 appearances so far in all competitions before Saturday's match.
Lockyer could now face a battle to resume his career after the latest health scare.
A statement from the Premier League read: "The Premier League match between AFC Bournemouth and Luton Town FC has been abandoned due to a player medical incident.
"Our thoughts are with Tom Lockyer and all players involved in today's match."
The Wales national team posted on X, formerly Twitter: "Our thoughts are with Tom Lockyer".
