Dr Sage concluded that Mr Scollay died as a result of internal and external blood loss.
He lost about 2.2 litres of blood - about half his total blood level. If someone suffers 20 per cent blood loss, it can be fatal, Dr Sage said.
"A stab wound like this causes massive bleeding,'' he told the court.
"This is the sort of wound that if you sustained it on the hospital doorstep you might survive. Absolutely no guarantee you would survive it. If you are 5 or 10 minutes from [hospital], your chances of survival are very bleak indeed.''
There was no evidence of defence wounds on his hands or arms that normally would be indicative of someone trying to fend off a knife-wielding attacker.
Dr Sage's evidence concluded the Crown case. The defence will now open its case.
Mrs Scollay, 45, stabbed her husband after becoming frustrated with his mental illness and worried he would never change.
In the early hours of Sunday, February 10 last year, she returned home after a night out drinking.
She took a large kitchen knife into the bedroom where her husband of 20 years was sleeping.
"She took her husband by his shoulder as he lay sleeping on his side, rolled him onto his back, got on top of him, straddling him as he was still half asleep, brought the knife up and stabbed him in the chest, a deep wound that penetrated his heart,'' Crown prosecutor Mark Zarifeh earlier told the jury of seven women and five men.
The couple's only child, their son Louis, was woken by her "almost scary'' shrieking.
He found his father lying "limply on his back with blood coming out''.
Mrs Scollay was apologising to her husband and pleading with him to stay alive.
The trial, before Justice Cameron Mander, continues.
The judge will sum up the case tomorrow morning.
