John Heard died of a heart attack.
John Heard
The 'Home Alone' star - who played Peter McCallister in the film franchise - was found dead in a hotel in Palo Alto, California, last month aged 71, and his cause of death is confirmed to have been a heart attack brought on by heart disease.
According to TMZ, the Santa Clara County Medical Exmainer's Office discovered John died of a "sudden cardiac death due to atheroscerotic and hypertensive heart disease" after they carried out an autopsy.
John was staying at the hotel to recover from a minor back operation he had two days before at Stanford Medical Center, but the surgery "did not play a role in his death".
The star's toxicology results have not been made public.
The actor - who also starred in movies 'The Pelican Brief' and 'In the Line of Fire' - was found by a maid and pronounced dead at the scene when paramedics arrived.
John has been laid to rest in a plot at the Lady Of Hope Church in Massachusetts, beside his son Max, 22, who died following an overdose in December 2016.
His former wife Lana Pritchard recently said: "John was laid to rest next to Max which was a sweet gesture. The funeral was arranged by his sister, Cordis, and only a very few family were in attendance.
"I co-operated with the family the best I could after his sudden death but we are totally in the dark about any will and testament John may have had.
"I'm sad because I would have liked to have paid my respects as I was very close to him right up until he died although there could be a service to commemorate him by his friends in Los Angeles later this month."