12:09 PM PT -- Susan's husband, Harvey Swindall tells TMZ ... Susan passed away from heart attack Saturday morning. He recalls her as the most amazing person he'd ever met, adding he'll miss her very much.

Susan Backlinie, who played one of the most memorable roles in "Jaws," has died ... TMZ has learned.

The longtime actress and stuntwoman passed away at her home Saturday morning in Ventura, CA ... according to Matthew Templeton, the agent who handled her convention bookings. He says the cause of death has not been determined yet.

SB got her start in the acting world in 1975 with the role of Chrissie Watkins in Steven Spielberg's shark flick. She's the woman who goes skinny dipping in the ocean in the opening scene ... and gets savagely yanked back and forth by the shark before she's eaten.

The scene, and Susan's role, became iconic when the movie turned into Hollywood's first true blockbuster. It also made millions of people stop swimming in the ocean!

The scene took a couple days to shoot, and in an interview last year, Susan remembered the water being totally freezing, but added ... she's seen "Jaws" a ton and clearly has lots of love for the movie.

She partnered with Steven Spielberg to spoof the scene a few years later in one of his less beloved movies, "1941."

Backlinie went on to do a lot of stunt work in films and TV. Some of her credits include "The Great Muppet Caper," "Day of the Animals," and the TV show "The Fall Guy."

But, it's her "Jaws" role that always made her a fan favorite on the convention circuit.

Susan is survived by her husband, Harvey. She was 77.

RIP