The father of a Perth woman who fatally stabbed her de facto after he violently "lost it" during a dispute over loud music was left with injuries including bite marks, a court has heard.
Tracey Bridgewater, 41, is on trial in the West Australian Supreme Court, charged with the manslaughter of Nicholas Josephs, 44, at their Hamilton Hill home in September 2018.
Mr Josephs became violent after Bridgewater threatened to call police over heavy metal he refused to stop blaring and he assaulted his much-smaller girlfriend before turning on her parents, who were aged in their 60s.
Prosecutors say he pushed Bridgewater, punched her father in the face - fracturing an eye socket - and may have kicked her mother after pulling her to the ground by her hair.
But the defence team argues Mr Josephs' attack was so "extreme and psychotic" - including pinning down and headbutting Bridgewater's heart patient father - she believed he meant it when he shouted he would kill them all and her dogs.
Paramedics who were called to the house after Bridgewater phoned triple zero saying she had stabbed Mr Josephs in the chest testified on Tuesday.
Simon Klass said crews tried to resuscitate the victim as he lay in a pool of blood in the entrance area of the house, while Bridgewater was out the front in a police van as her injured parents were assessed.
Mr Klass asked her how many times she stabbed Mr Josephs and she replied: "Just once ... it was self defence".
Louise Biggs said the father was dizzy, had bite marks on his inner right arm, his left eye was so swollen it was almost shut and his clothes were bloodied.
Matthew Rolfe said the mother was in pain with injuries to her ribs and left shoulder, and was "very emotional".
Notwithstanding anything the deceased had done, Bridgewater did not call police and instead "drastically escalated an already tense situation" by deliberately stabbing Mr Josephs, prosecutors say.
According to the defence, Mr Josephs had a history of irrational jealousy and posted comments on social media on the night of his death included "no-one gets out alive" and "others will always cheat no matter how good things are".
Bridgewater's parents were visiting from the UK to celebrate her birthday and to meet Mr Josephs.