Hieatt, 48, has pleaded not guilty in the High Court at Auckland to the murder of Nuttidar Vaikaew, claiming that the killing amounted to manslaughter and that he was provoked.
Her badly decomposed body was found in a bed in her Western Springs, Auckland, apartment, close to a month after her death, with Hieatt still living there.
Hieatt, a computer programmer, told the court today he and Ms Vaikaew, a Thai sex worker, had been in a dysfunctional relationship which he had been trying to break up for years.
He had taken numerous trips to see another woman in Thailand to try and get away from Ms Vaikaew but returned to live with her in March 2009.
She made him leave the house during the day so she could see her clients, so Hieatt spent his days working on his computer at his storage unit, at the local library and in a nearby park.
Hieatt was not happy about this because he was paying more than half the rent so felt he should be able to work from home, and wanted her to stop working as a prostitute.
On April 17 they got into a heated argument about this situation and she started screaming at him.
"I couldn't take it anymore - being shouted at, ordered around, talked down to, treated like crap - I just wanted her to shut up," he said.
He fetched some masking tape and tried to put it over her mouth but she tore it off and scratched his face, he said.
"She was on fire. She was just wild, angry and ready to fight."
Hieatt said he "just lost it" and punched her several times in the head and chest.
"She struggled out of bed, sort of half fell out of bed and headed towards the door and she started shouting 'help, help, he's attacking me', stuff like that."
He dragged her back to the bed, held her down and muffled her cries with a pillow or blanket.
She said "you want kill me" - which Hieatt said was more of a statement than a question - and he replied that he did not.
There was a box of "bondage gear" under the bed including some leather handcuffs, which he attempted to restrain her with.
When this failed, he got a rope out of the box to tie her to the bed with at which point she repeated: "you want kill me."
"It's like something happened and all of a sudden I heard my voice saying 'yes, I'm going to kill you'. I put it around her neck and tied a knot. I watched my hands, I couldn't stop it, it was like I was watching a movie, I couldn't stop it happening," he said.
Hieatt broke down at this point.
His lawyer, Peter Kaye, said Hieatt had a difficult childhood and his brother committed suicide in the mid 1980s - an event which had a profound affect on him. After that, he began using marijuana and seeing prostitutes on a regular basis.
Part of Mr Kaye's case is the defence of provocation, which was abolished by the Government last year but could be available to Hieatt because the alleged offence took place before the law change.
Hieatt will continue giving his evidence tomorrow.
