Hayden Panettiere's Autopsy Complete, No Signs of 'Trauma'

Hayden Panettiere's autopsy showed no signs of trauma ... according to the Greenville County Coroner's Office.

The coroner released some details from the autopsy in a press release Monday, saying ... "no signs of trauma were discovered that would have contributed to the death. The cause and manner of death remain pending further investigation and the completion of additional studies."

The rest of the release reiterates information we've already reported ... first responders arrived at a residence in Greenville, South Carolina, after receiving a call about a woman in cardiac arrest Sunday.

They rushed to the scene and performed advanced cardiac life support measures ... but they weren't able to save her life. Hayden was pronounced dead at 2:32 PM.

Dispatch audio revealed first responders were sending medics to Hayden's location to perform CPR on someone who may have overdosed. We confirmed Narcan, a medication administered to reverse the effects of an opioid OD, was administered. It's unclear if the Narcan was used on Hayden or someone else -- two ambulances rushed to the scene.

The Greenville County Coroner says the investigation into Hayden's death is ongoing.

Hayden first gained fame as a child star in the late 1990s and early 2000s ... and appeared in some beloved films and TV shows over the last 3 decades, including "Heroes," "Nashville," and the 'Scream' franchise.

She was just 36.