The woman was afraid that Byrne was going to harm her and her current partner, the court heard.
Mark Byrne (50) told the terrified woman that he had “done 10 years” before in prison and he had no problem going back to prison for the “right reasons”.
In a previous attack in 2013, Byrne used a kitchen knife to inflict a life-threatening kidney injury on his then partner's new boyfriend as he struggled with the couple when they returned to their flat where Byrne had been waiting for them.
Sentencing him in October 2014, Judge Martin Nolan jailed him for seven years.
Last month, Byrne, of Coburg place, Seville Place, Dublin city, pleaded guilty at Dublin Circuit Criminal Court to harassment of the woman on the evening of February 12, 2021 into the next morning.
At a sentence hearing on Monday, Garda Alan Roche told Fiona Crawford BL, prosecuting, that from just before 8pm in the evening to 1.20am, Byrne left 12 voice messages on his ex-partner's mobile phone.
He told her: “I'm out three years from prison for stabbing a c*nt - for the right reason. The next time I go will be for the right reasons”.
He told her that he knew the gardai would end up hearing these messages, “as evidence after the fact” and it would be “too late” then.
He told her he was “stupid enough to make a point” and that she wasn't “in control anymore”.
The woman was afraid that Byrne was going to harm her and her current partner, counsel said.
She stayed up all night with a baseball bat and had visions of being stabbed. She went to gardai the next morning.
Gardai went to Byrne's home in the city centre and during the course of executing a search warrant, armed gardai shot his pit-bull terrier dead.
A search of the house uncovered cannabis herb with a street value of just over €8,000, alongside bagging materials, weighing scales and cash.
Gda Roche agreed with Oisin Clarke BL, defending, that Byrne was living an isolated life at the time, living under lockdown on his own in the family home after his mother had recently died.
Counsel said his client had nothing to do, nowhere to go and was drinking at home.
Gda Roche agreed that Byrne was mortified when he heard the content of the messages he had left played back to him during garda interview.
He expressed remorse and told gardaí: “I'm not crazy, I'm hurt, I'll get over it.”
Judge Nolan said that the very threatening messages were calculated to terrify the woman and they did so.
He noted Byrne was suitably remorseful when confronted with the messages. Judge Nolan imposed a three and a half year prison term and ordered that Byrne have no future contact with the victim.
At the same hearing, Byrne also pleaded guilty to possession of cannabis for sale or supply at his home on February 14, 2021.
Judge Nolan imposed a three-and-a-half year prison term for this, to run concurrent with the other sentence.
He backdated both sentences to February last year, when Byrne went into custody.
In 1997, Byrne received a seven year prison sentence when he admitted possession of cannabis resin valued at £40,000 for supply on March 23 1996, and possession of cocaine on the same date, at an address in Sheriff Street.