A man has been found guilty of manslaughter for killing a heart surgeon in a one-punch attack at Box Hill Hospital in Melbourne's east last year.

Key points: Surgeon died when life support switched off a month after attack

Surgeon died when life support switched off a month after attack He had asked Esmaili to stop smoking in non-smoking area outside hospital

He had asked Esmaili to stop smoking in non-smoking area outside hospital Defence argued switching off life support caused death, not the punch

Joseph Esmaili, 24, punched Patrick Pritzwald-Stegmann in the head during an argument in the foyer of the hospital in May 2017.

The 41-year-old surgeon was knocked unconscious and fell backwards, hitting his head on the tiled floor.

He died in hospital a month later.

The pair began arguing after the surgeon asked Esmaili and his friends to stop smoking in a non-smoking area outside the hospital, the Victorian Supreme Court trial was told.

CCTV was played to the jury which showed the men arguing in the moments leading up to the punch.

Surgeon Patrick Pritzwald-Stegmann died in hospital a month after he was punched. ( Epworth Healthcare )

Witnesses gave evidence Esmaili was asked to leave the hospital, but responded by telling Mr Pritzwald-Stegmann, "You need to suck my d***".

Mr Pritzwald-Stegmann was then overheard angrily retorting: "You just spat in my face."

The families of both Mr Pritzwald-Stegmann and Esmaili were in court to witness the verdict being handed down and did not react when it was read out.

Esmaili has been remanded in custody and will return to court in March for a plea hearing.

'I wasn't trying to hit him hard'

During the trial, defence barrister John Desmond argued Esmaili had acted in self-defence when he punched the surgeon, who put his bag down on the floor during the confrontation.

"Why is [Mr] Pritzwald-Stegmann freeing up his hands at that point?" Mr Desmond asked.

"At the very least … it would be a reasonable inference on Esmaili's part that the doctor's about to punch him."

But prosecutor Brendan Kissane QC disputed the surgeon had done anything to suggest he was going to punch or attack Esmaili.

"We accept that he didn't back down, but … that doesn't excuse what effectively was an attack on him," he told the jury.

"When [Esmaili] decided to throw the punch … there was no threat to the welfare of the accused man.

"What Mr Pritzwald-Stegmann was doing was attempting to get him to leave."

The court heard Esmaili fled from the hospital after punching the surgeon and told his friends outside that they, "needed to leave because he had just hit someone".

He was arrested the following day after his father saw the media reports about the incident and contacted police.

In a recorded police interview played to the jury, Esmaili told detectives: "I wasn't trying to hit him hard, I shouldn't have hit him in the first place, I know."

Mr Kissane said Esmaili never mentioned to investigating police he had felt frightened or concerned he was about to be attacked.

Withdrawal of life support caused surgeon's death: defence

Mr Desmond also argued Mr Pritzwald-Stegmann's death was caused by his family's decision to withdraw life support, rather than the punch itself.

"It was a deliberate decision made by collective medicos in conjunction with his wife … to withdraw medical treatment and facilitate death," he told the court.

"What Esmaili's caused with his punch is serious injury and that was the setting, and no more, by which doctors and the family … formed the view, without being critical of them … we will terminate this life.

"That death should not be visited upon Joseph Esmaili in those circumstances."

But Mr Kissane told the jury they did not have to be satisfied the punch was the sole cause of Mr Pritzwald-Stegmann's death, but a "substantial and operating cause" of his death.

"The medical intervention might have put death off for a period of time, but when ultimately he died, the substantial and operating cause was the head strike," he said.

"You don't have to be satisfied that it was the only cause, you only have to be satisfied that it was a substantial and operating cause."