A Ranby prisoner took mamba before he told a nurse he wanted to kill his ex-partner while serving a sentence for assaulting her, a court heard.
Luke McMahon became aggressive and clenched his fists during a routine interview with a senior mental health nurse, on May 21.
"He said he would seek his ex-partner and kill her," said prosecutor Donna Fawcett.
He blamed the NHS for his situation and told the nurse to write down what he was saying.
"I will give people what they want," he said, and the nurse believed he would carry out the threat, said Ms Fawcett.
McMahon received a 16 month prison sentence for using violence to secure enty into his ex's home and assaulting her, causing actual bodily harm.
He broke into her home and broke her nose after she brought an end to their three-month relationship, said Ms Fawcett.
The court heard McMahon's ex had moved home six times with her children, and had "lost contact with family ans friends as she "no longer knows who to trust."
In a statement from June 18, she said: "His threat that he will finish the job off is continually on my mind. I will continue to be looking over my shoulder for some time."
Melanie Hoffman, mitigating, said: "There was never any intention to carry out the threat."
She said he suffered emotional and physical abuse from his parents and was taken into care at the age of ten, using drink and drugs three years later to deal with depression.
"It was a very emotional topic for him," Ms Hoffman said. "He is very concerned about the welfare of his children."
McMahon, 26, formerly of Woodborough Road, Nottingham, admitted making the threats, when he appeared at Mansfield Magistrates Court, on Wednesday.
He was given unconditional bail to appear at Nottingham Crown Court, on August 7, for sentencing.