In new documents obtained by TMZ ... Maryland's Chief Medical Examiner declared the internet personality died from cardiac arrhythmia due to myocardial fibrosis -- which means she essentially had an irregular heartbeat caused by scarring on the heart muscle.

Her toxicology report found no signs of alcohol ... but she did test positive for Diphenhydramine -- a common antihistamine, marketed as Benadryl among other brand names -- and Mitragynine ... an alkaloid often used for pain management.

There had been quite a bit of speculation regarding Kyle's death in recent months ... especially after it was revealed her parents called in for a welfare check after seeing one troubling post on her TikTok account.

Kyle was best known for posting Hollywood blind items and showbiz gossip on the social media platform ... but it's unclear which specific upload sparked concern from her loved ones.

As TMZ previously reported ... Annapolis PD made their way to Kyle's apartment in April after her parents hadn't heard from her in a while ... where she was discovered deceased.

Kyle's loved ones later confirmed her death on social media ... with Kyle's sister Lindsay telling fans the cause of death remained unclear -- further fueling speculation about her passing.

Lindsay added at the time ... "i know she touched so many people with her humor, intelligence, beauty, gossip activism, athleticism and more - she had so many gifts."

Kyle was only 36.