Sources tell TMZ ... Lisa was pronounced dead at the L.A. area hospital where she was taken after suffering cardiac arrest Thursday morning.
TMZ broke the story ... Lisa was rushed to the hospital after her housekeeper found her unresponsive at her Calabasas home. Her ex-husband, Danny Keough, was there and performed CPR on her until paramedics arrived and took over -- they administered at least one dose of epinephrine during resuscitation efforts.
We're told EMTs were able to regain a pulse before she was transported to the hospital.
A rep for Priscilla Presley, Lisa Marie's mother, tells TMZ ... "Priscilla Presley and the Presley family are shocked and devastated by the tragic death of their beloved Lisa Marie. They are profoundly grateful for the support, love and prayers of everyone, and ask for privacy during this very difficult time.”
As you know, Lisa Marie's the daughter of Elvis and Priscilla ... born exactly 9 months after her parents tied the knot.
She became joint heir to Elvis' estate with her grandfather and great-grandmother after he died of a heart attack in 1977.
LMP followed in her father's footsteps, becoming a singer/songwriter and dropped her debut album, "To Whom It May Concern" in 2003. The record reached number 5 on Billboard's album chart, and earned gold certification.