Heather Elizabeth Parkhurst -- an actress who's appeared in "Alpha Dog" and "Beverly Hills Cop III" -- damn near got her arm torn off when her pit bulls turned on each other, mauling her in the process.

Heather's fiance, Mark Nason, tells TMZ ... the scary incident went down Friday night at their West Hollywood home. We're told Heather was petting their 7-month-old pit, Baby, when their other pit bull, 8-year-old Buddha, suddenly appeared to get jealous and growled.

And, that's when Baby and Buddha lunged at each other but Heather's right hand and arm got caught in the middle of the violent melee.

The attack left Heather -- who's also acted on TV shows like "NYPD Blue" and "Married with Children" -- a bloody mess. She was rushed to the hospital to treat gruesome injuries, including crushed bones in her hand, torn ligaments and other deep cuts throughout her arm.

We're told doctors inserted pins and stitched up her arm but she remains hospitalized.