A 12-year-old California girl found unconscious after a ride on a Las Vegas Strip roller coaster died Tuesday.

The Clark County coroner's office said it could be several weeks before a cause of death is determined for Catlynne Shaw of Union City, Calif.

Authorities initially thought Shaw suffered a heart attack during the July 16 ride on the Canyon Blaster at the Circus Circus Adventuredome.

VIDEO: Click to watch Dr. Manny discuss what may have caused Catlynne's death.

An off-duty Clark County firefighter was credited with helping resuscitate Catlynne before paramedics arrived. She was taken to University Medical Center, where she later died.

A spokeswoman for MGM Mirage Inc., which owns Circus Circus, said the roller coaster opened in 1993.

It can reach a maximum speed of 55 miles per hour and includes a 45 degree drop.