A longtime Manhattan building superintendent suffered a fatal heart attack during a brawl with a bike messenger on Tuesday, authorities said.

Roger Balan, 58, the super of 432 Park Ave. South, and the messenger, Devon Givens, began fighting outside the building between East 29th and East 30th streets at around 12:15 p.m., authorities and witnesses said.

“The [bike messenger] threw the first punch and the [super] was hitting back,” said a witness, José Reyes.

A woman tried breaking up the fight, but she, too, wounded up being punched, according to witnesses.

The super suddenly collapsed, and the messenger coldly rode off to make another delivery, cops said.

Medics rushed the Merrick, LI, husband and father of two to Bellevue Hospital, where he died.

It’s unclear what sparked the violence. A law-enforcement source said the initial confrontation began in the 16-story building’s elevator and then moved onto the street.

Balan’s family was devastated. “He’s a peaceful man. I can’t even imagine him in a fight,” said his sister-in-law Nadine Kalogeras. “We are just stunned.”

Cops charged Givens, 35, with manslaughter.