The 52-year-old faced questioning at Sydney's Downing Centre Local Court on Thursday over the September 2021 incident, during which police allege he knocked the woman to the ground and pinned her down.
O'Keefe also allegedly pushed the woman into a door frame, causing scratches to her arm.
He is facing charges including domestic assault, drug possession, breaching an apprehended violence order and resisting arrest.
But O'Keefe told the court the woman, who cannot be identified for legal reasons, inflicted the scratches on her own arm during an argument.
He was accused of saying "good riddance" to the woman and making repeated spitting gestures towards her after knocking her down.
"None of this happened," O'Keefe said.
The pair had been in COVID-19-related isolation at the time and had argued over whether O'Keefe called the woman's daughter a "c***", the court heard.
"We both know that she can be a manipulative little s***, but I did not call her a c***," O'Keefe said he told the woman at the time.
On that night, O'Keefe said he began experiencing symptoms including dizziness and profuse sweating, which caused him to believe he was having a heart attack.
He was later transported by ambulance to hospital and was diagnosed with a respiratory tract infection before being released a short time later.
Andrew O'Keefe is facing multiple charges including domestic assault and drug possession.
O'Keefe had previous charges dismissed on mental health grounds following an incident in January 2021 during which he slapped the woman and spat in her face by his own admission.
That dispute was sparked after the woman felt what she thought was an "ice pipe" in O'Keefe's pocket.
The troubled former Seven Network presenter said the item was in fact a spoon and a lighter.
Regarding the January incident, O'Keefe said the pair had attended a party together during which she became quite drunk, while he only consumed a moderate amount of alcohol.
He said as they went to leave the party together, the woman felt what she thought was an implement for smoking methamphetamine in his back pocket.
"She said, 'why the hell did you bring that?'," O'Keefe told the court.
"She could have been forgiven for thinking that. In the past there had been incidents."
After returning to the woman's home, the pair continued to argue and O'Keefe said he asked the woman to call him an Uber to get home as he was "flat broke".
When she refused to do so, O'Keefe said he called her "f***ing heartless" and suggested the relationship should end.
"She said, 'this relationship's never meant anything to me anyway', which I was very hurt by," he said.
O'Keefe said he then spat in the woman's face to "illustrate (that) what she said to me was a spit in the face".
"(That is) something I'll regret for a very long time," he told the court.
Later, the woman also threatened to publicly substantiate looming allegations about the then-Deal or No Deal host's drug use, including a former driver telling media he witnessed O'Keefe smoking ice in the back of his car.
O'Keefe told the court the woman threatened to tell the Seven Network and his ex-wife he was an abusive "junkie" who saw "hookers".
"Then I slapped her ... once across the face," he said.
O'Keefe added when the woman continued to say she would make public allegations against him he went "slap, slap, slap" with his other hand.
The hearing continues.
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