A man told police he tried to revive his elderly mother for about eight hours before calling emergency services as she lay stricken from his deadly blow with a pot plant.

David Andrew Mapp is accused of murdering his 82-year-old mother Colleen Wilson at Tumbi Umbi on the NSW Central Coast on July 28, 2022.

After killing his mother, Mapp pawned her TV and whipper snipper for AU$200 (NZ$221), money he used to buy heroin, a court was told on Tuesday.

Wilson was previously forced to pay AU$700 (NZ$772) to get her TV back after her son pawned it, the NSW Supreme Court jury heard as his trial got under way.

The 59-year-old claims he did not intend to kill his mother and at the time was suffering from severe anxiety and heroin withdrawals.

Prosecutors allege Mapp argued with his mother on the morning of her death before he went outside the house, retrieved a pot plant and hit her on the head.

She fell to the ground and later died.

Mapp also allegedly applied pressure to his mother's neck while she was lying down — a matter disputed by the defence.

His earlier guilty plea to the lesser offence of manslaughter was rejected by prosecutors.

Prior to killing his mother, Mapp spoke to a woman named Lynette Perkin, who had offered him some cleaning work at her home in exchange for money.

Perkin was expected to give evidence that during the conversation Mapp said: "Mum doesn't want me."

His barrister Sarah Talbert said Mapp had used heroin since he was 16 years old and relied on his mother for support, but their relationship had deteriorated to the point she was "angry, frustrated and fed up".

At the time of his mother's death, Mapp was suffering heroin withdrawals as well as a severe generalised anxiety disorder — a condition that would have affected his ability to control himself and make sound judgments, she said.

"It's the defence case that Mr Mapp, in that context, threw the potted plant at his mother and it hit her on the head and caused her death," Talbert said.

Immediately after killing his mother, Mapp took 10 Valium tablets, which likely would have affected his memory of events, the barrister said.

Shortly after 5pm, Mapp called triple zero to report a body, saying he and his mother had a "bad argument" and he had been trying CPR all day in an attempt to revive her.

When emergency services arrived, Wilson was lying on the floor underneath a red blanket with blood and soil surrounding her, and she was cold to the touch, the jury heard.

Mapp told officers he tried to revive his mother, had a coffee and tried CPR on and off for around eight hours before calling for help.

The trial continues.