It happened at 2 p.m. Saturday when the 41-year-old woman was at Tapia Park in Malibu Creek State Park, according to Lt. Greg Evans of the Malibu-Lost Hills Sheriff's Station.
She was pronounced dead at the scene, Evans said. Her identity has not been disclosed.
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The woman started hiking at 8 a.m. Saturday, said Malibu Search and Rescue Team Leader David Katz.
"A few hours later, she suffered a reported seizure,'' Katz said. "CPR was initiated and performed for 20 to 30 minutes before she was
pronounced.''
She died at 2:10 p.m. according to the Los Angeles County coroner's office.
An advisory closing the trails added that Malibu Search and Rescue responded to several heat-related rescues.
"PLEASE DO NOT #HIKE IN THIS #HEATWAVE," Malibu Search and Rescue tweeted.
An excessive heat warning remains in effect until 8 p.m. Monday.
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City News Service contributed to this report.