Lena Kasparian leaves the Supreme Court today in Sydney. Kasparian is on trial for the murder of her partner Marc Zartarian.

Lena Kasparian leaves the Supreme Court today in Sydney. Kasparian is on trial for the murder of her partner Marc Zartarian. Photo: Mick Tsikas

A woman who stabbed her de facto partner at her Wetherill Park home has pleaded not guilty to murder on the grounds of self-defence.

Lena Kasparian, 33, claims Marc Zartarian was drunk and aggressive towards her after they returned home from a first birthday party at the Belrose Hotel on May 1 last year.

Today, a NSW Supreme Court jury of nine women and three men heard a kitchen knife entered Mr Zartarian's chest, causing a 15-millimetre stab wound, which damaged a ventricle in his heart.

Ms Kasparian then locked herself in the laundry while Mr Zartarian walked around the house making phone calls.

When he called out that he was having trouble breathing, Ms Kasparian said she left the laundry and phoned triple-0.

The jury was played a recording of the call. "He's fine, it's just a small stab wound," Ms Kasparian says.

But the court heard that, when police arrived, Ms Kasparian was distressed and hysterical and told ambulance officers to "keep him alive, keep him safe".

She said he hit her with a stainless steel saucepan and she picked up the knife to protect herself. She allegedly told him to get back but he moved towards her, saying: "Stab me, just do it."

"Yes, I stabbed him but he was attacking me so I had to," she told police. "He's going to live isn't he? I don't think I can have this on my conscience."

Mr Zartarian died in hospital on May 6, 2011 after suffering a brain injury caused by loss of oxygen following the stabbing.

The Crown prosecutor, Pat Barrett, said Ms Kasparian inflicted the stab wound with the intention to cause grievous bodily harm or that she did so foreseeing the risk that death could occasion from stabbing him in the chest.

But Ms Kasparian's barrister, Peter Doyle, said a mobile phone recording of an interview his client gave to police soon after the incident would demonstrate the "emotion" she was experiencing and show that "the issue of self-defence is a real issue".

The trial before Justice Peter Garling continues.