Oct.12 (GMM) Maria de Villota's post-mortem has confirmed reports the former Marussia tester died of natural causes.
International publications say the 33-year-old died of a heart attack after a suspected brain haemorrhage in a Seville hotel early on Friday.
Germany's Welt newspaper said Spanish authorities are investigating, but rumours de Villota could have committed suicide are wide of the mark.
The report also said no medications or drugs were found in the hotel room or de Villota's body.
"It was absolutely natural causes," a forensic medicine spokesman said in Seville after the autopsy.
Spain's EFE news agency said Isabel de Villota suggested her sister's death was related to her serious head injuries sustained in the Marussia test crash last year.