The coronial inquest into the death of schoolboy Stephen Dudley has heard that an assault on the 15-year-old was the "trigger of his death".
Stephen died in June 2013 following a fight with two brothers, both boys aged 15 and 17 at the time, who were later discharged without conviction after a medical examination found Stephen had an undiagnosed medical condition known as cardiac sarcoidosis.
Forensic pathologist Dr Paul Morrow presented his findings to the inquiry and based on his opinion said the cause of death was "cardiac arrhythmia".
Earlier in the inquiry witnesses described seeing strange veins on Stephen's neck following the assault.
Dr Morrow said that was a possible sign of "severe cardiac failure".
"What this young man was observing was heart failure due to [Stephen's] arrhythmia, that would of been a sign of that."
He said "it's hugely likely the stress of the assault" may have been a contributing factor.
Dr Morrow said Stephen showed no signs of having any problems with his heart and based on his opinion the stress of the event caused the 15-year-old's death.
"In Stephen's case I was lucky enough to identify what the extra factor may have been through forensic pathology, that event was the trigger of his death - sarcoidosis was a reason to say why."
During Stephen's autopsy Dr Morrow noticed some scarring in the conduction system in the heart.
Cardiac sarcoidosis in Dr Morrow's opinion can leave behind some scarring, and the disease can also be life threatening.
The inquest at Auckland District Court is expected to conclude today.