Article continues below advertisementLegendary actress Catherine O'Hara's cause of death has been revealed less than two weeks after her death at 71 years old. The Schitt's Creek star died of a blood clot in her lungs, according to the Los Angeles County Medical Examiner's Office, a news outlet reported on Monday, February 9. Her immediate cause of death was listed as pulmonary embolism, with rectal cancer as the underlying cause.