The man, whose name has not yet been released from the Lake County Sheriff-Coroner's Office, died at the scene.
He had been hang gliding in an area several miles north of Upper Lake in the Middle Creek area off of Elk Mountain Road, officials reported.
Northshore Fire Battalion Chief Pat Brown said they responded to a medical call at around 1 p.m. Saturday.
They found the man had crashed his glider, but Brown noted that the crash wasn't a hard one.
What appears to have taken the man's life was a heart attack while he was still in the air, said Brown.
Brown said firefighters were unable to revive the victim.
Tamara Schmidt, spokesperson for the Mendocino National Forest, said the incident did not happen on US Forest Service Land.
She said the forest offered to assist Northshore Fire with an engine, but it wasn't needed at the call.
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