A Quebec cardiologist charged with two counts of first-degree murder admits he stabbed his two children in 2009, but claims it wasn't a premeditated act.

Guy Turcotte's defence team made the admission Monday, at the cardiologist's double murder trial in Saint-Jérôme.

In a statement filed by his defence lawyer Pierre Poupart, Turcotte admits he committed an illegal act and caused the death of his two children.

Olivier (5) and Anne-Sophie (3) were stabbed to death by their father, he admits. (CBC)

But Turcotte plans to fight the claim that the killings were premeditated.

Poupart told the jurors that they will have to determine Turcotte's state of mind at the time of the crimes, and whether he knew what he was doing.

Turcotte's children — five-year-old Olivier and three-year-old Anne-Sophie — were found stabbed to death on Feb. 21, 2009, inside a house their father rented in the Laurentians.

Turcotte was also found in the house, under a bed, after he ingested windshield washer fluid.

He was charged and found fit to stand trial at a preliminary hearing last year.

Failed marriage on doctor's mind

Turcotte sobbed in court as Crown prosecutor Claudia Carbonneau outlined the details of the double slaying.

A crime scene technician gave jurors a view inside the home: two knives, two bloodstained beds, a near-empty windshield washer container in a bathroom and vomit on the floors.

Turcotte's mother Margaret Fournier testified Monday about the last phone conversation she had with her son before the children were killed.

Turcotte, a cardiologist, faces two first-degree murder charges. (Canadian Press)

Turcotte lamented his failed marriage to Isabelle Gaston, from whom he had separated a month earlier.

Fournier said her son sounded depressed and told her Gaston was cheating on him.

"It has been going on for weeks," Fournier quoted her son as saying. She said he told her "it was happening in my house, in my bed."

His mother advised him to look forward, but her son didn't seem to hear her. But then he said something that struck Fournier as out of character.

"I love you, tell Dad I love him," Fournier recounted, remembering her son repeating those words over and over during the hour-long chat.

"When I heard that discourse, I was afraid he was about to take his own life," she said.

Fearful he'd been drinking, Fournier wanted to drive to her son's that night, but her husband said to wait.

Fournier arrived the next day to find no grandchildren in sight, the doors locked and the shades drawn at the single-family dwelling in an isolated rural neighbourhood in Piedmont.

"Maybe my husband still had hope [things were OK], but I had no hope at all," she testified.

Fournier's chilling 911 call pleading with police to hurry to the rented home was played in court late Monday, provoking more sobs from Turcotte.

If found guilty, he could face life in prison.

About 30 witnesses are expected to testify at the trial, including police, ambulance technicians and family.

Gaston, a doctor herself, is also expected to take the stand.

The trial is scheduled to last between six and eight weeks.

Police tape blocks access to a house in Piedmont, Que., where the bodies of two young children were found on Feb. 21, 2009. (Graham Hughes/Canadian Press) With files from The Canadian Press