Dan Rivera — the paranormal investigator on a creepy “Annabelle” doll tour who died completely out of the blue in the “haunted” Civil War battlefield town of Gettysburg — had a history of heart issues … and the coroner says his death was cardiac-related.

Rivera’s autopsy results have been released by County of Adams Coroner Francis Dutrow, and we’re told Dan died from natural causes.

As we reported … Dan was in Pennsylvania for his “Devils on the Run” tour — hauling the infamous Annabelle doll across the country — when he died July 13 in his hotel room.

We’re told Dan had a known history of cardiac issues, which were consistent with the autopsy findings.

Dan was a fixture in the paranormal world, as the lead investigator for the New England Society for Psychic Research … and he’d built serious ghost-hunting cred and a robust social media following off the eerie superstitions tied to Annabelle’s haunted history.

The story of the supposedly possessed doll Anabelle inspired the 2013 movie “The Conjuring,” and the 2014 film “Annabelle.”