An unfortunate movement in heart muscles caused a Whangarei man's healing stab wound to reopen and send him into a form of heart failure, a forensic pathologist has testified in court.

Dr Paul Morrow conducted a post-mortem examination on Brandon Panapa-Ripia, 17, a day after he died on November 20, 2012 while shopping at The Warehouse in Whangarei.

He had three weeks earlier been stabbed with a kitchen knife by his girlfriend Shaylene Wharerau, 22, who is on trial in the High Court at Whangarei facing a charge of murder. She faces alternative charges of wounding with intent to cause grievous bodily harm and wounding with reckless disregard.

Wharerau has admitted stabbing Mr Ripia in the chest during a domestic dispute over a smashed cellphone and access to a social media site on October 30, 2012. Her defence is that it was an accident.


Mr Ripia had surgery in Auckland after the stabbing but died three weeks later.

In his evidence before the jury yesterday, Dr Morrow said Mr Ripia died due to bleeding around a sac that surrounded his heart as a result of an old stab wound.

Dr Morrow explained that a stab wound was a form of sharp force and although it may seem relatively short on the surface, it may penetrate deep inside the body.

Dr Morrow said unlike the exterior, the interior edges of the sac had not completely healed.

"What happened was that as the wound healed, scar tissues connecting the heart to its lining began to get stuck to the chest wall which pulled apart the healing wound," he said.

Dr Morrow said Mr Ripia was beginning to go into some form of a heart failure because of chronic bleeding when he died.

Lawyer Nick Leader, assisting defence counsel Arthur Fairley, asked him whether there was any presence of alcohol or drugs in the deceased's body to which he replied "none".

The defence will open its case on Monday.