'Tarzan' Star Ron Ely Cause of Death Revealed

Ron Ely -- star of the 1960s TV show -- "Tarzan" died from a heart issue ... TMZ has learned.

According to the death certificate, obtained by TMZ, Ron's official cause of death is listed as "end-stage heart disease."

End-stage heart disease is the most severe form of heart disease, occurring when the heart is too weak to pump blood effectively, and patients with the disease generally only live 6 to 12 months ... according to Massachusetts General Hospital.

The death certificate gives a nod to Ron's Hollywood career ... noting he spent 30 years in the entertainment business.

In addition to playing "Tarzan" on TV, Ron had acting credits on "Wonder Woman," "The Love Boat," "L.A. Law," "Doc Savage: The Man of Bronze," "The Friend Who Walked the West," and multiple other 'Tarzan' projects.

As we reported ... Ron's daughter announced his death back in October, saying he died peacefully September 29 in his home, surrounded by family.

The death certificate says Ron died at 7:04 PM and his body has since been cremated.

Ron was 86.