ANGELES NATIONAL FOREST — A man died Sunday after suffering what officials believed to be a heart attack while riding a motorcycle on Angeles Crest Highway.

The incident was first reported at 12:08 p.m. near mile marker 69 of Angeles Crest Highway, California Highway Patrol Office Tatiana Saquillo said.

The rider’s name and age were not available.

Initial investigation indicated the rider fell from his motorcycle, which collided with a guard rail, after suffering a heart attack, the officer said.

Rescuers rushed out via helicopter to treat the man, she said, however he was pronounced dead a short time later.

The Los Angeles County Department of Coroner is investigating the man’s cause of death.