The incident happened Wednesday night during a religious event in Brazil, where Pedro was performing a song when he suddenly fell to the floor unconscious ... and it's all on video.

Footage shows Pedro on the edge of the stage interacting with the crowd and singing the song "Vai Ser Tão Lindo" when he appears to lose his balance ... falling backward in front of his band and crashing to the ground.

Once Pedro collapsed onstage, folks rushed over to help him as the horrified crowd watched in shock.

Pedro was rushed from the concert venue to a nearby medical clinic, where he was pronounced dead ... and his record label, Todah Music, says he suffered a massive heart attack.

He was only 30.