The moment Robert Leahy's heart stopped beating is something his 17-year-old son will never forget.
Aquinas College student Logan Charters-Leahy watched his dad's body convulse as he suffered a massive heart attack.
"He looked like he was in hypoxic shock, his tongue swelled up and his hands curled up like they were cramping and he was convulsing," Logan told the Bay of Plenty Times.
"I checked if he was breathing, he wasn't and there was no pulse and I realised he was in cardiac arrest but there was no way I was leaving him. I kept thinking I was not going to let this happen."
Logan's mum Andrea Charters said she woke up about 6.30am on Anzac Day and heard Mr Leahy making "gurgling, gasping noises". She rolled over and saw his face was blue.
"I thought holy ****, we're in trouble. It was horrendous. I wouldn't wish that on anyone, seeing him lying there on the floor almost dead and not breathing."
As Mr Leahy lay on the bed in the family's Tirau home, Logan did a precordial thump on his chest - thumped it once quite hard - before he immediately began CPR. He said his mum was in hysterics so he told her and his 15-year-old sister Victoria to "get out".
Minutes later emergency services arrived and used a defibrillator to shock Mr Leahy's heart back into a rhythm.
Twelve minutes and six electrical shocks later, the father of two remained lifeless. His waning body was loaded into an ambulance and rushed to Waikato Hospital.
Mrs Charters said her son's actions were heroic and "so mature for someone who had only turned 17".
"It was just amazing. He was so calm and when the ambos got here they shocked him and rushed him into the ambulance and the driver said he was in a very critical way and they weren't sure if he was going to make it to Waikato.
"Victoria and myself, we followed in the car behind and Logan went in the ambulance with his dad. Then when they got him to Waikato they put him in an induced coma in Intensive Care. Doctors said they didn't know how long he'd been without oxygen so they gave us three possibilities - he would wake up and be fine, he would wake up but have brain damage, or he wouldn't wake up at all."
After an operation to insert a pacemaker and defibrillator into his chest, Mr Leahy spent three days in a coma before he woke.
Mrs Charters said: "We got to hospital about 3pm and the doctor said 'Don't be shocked when you see him'. So I was thinking the worst but we saw him and he was sitting up and he remembered us and I knew we were very lucky."
After 11 more days in hospital, Mr Leahy was allowed to return home.
Yesterday, he had a check-up at Waikato Hospital and was doing "fine", Mrs Charters said. He had a mild heart attack on January 16 and doctors have now diagnosed a heart condition which Mr Leahy would have had since birth. Mrs Charters said her husband had large burn marks on his chest and was recovering from broken ribs from the CPR. She was "so grateful" Logan was at home and she was "extremely proud of him".
Logan said he didn't have time to be stressed and his first aid training as a member of the Tirau volunteer fire brigade kicked into action, so he immediately knew what to.
St John district operations manager Jeremy Gooders said Logan's actions undoubtedly helped save his father's life.
"The survival rate of someone that goes into sudden cardiac arrest is about 10 per cent or just below. Sometimes a person is able to be brought back by one shock and sometimes it takes more shocks until the heart is back into a rhythm."
Mr Gooders said cardiac arrest patients had a "window of time" for CPR and ambulance officers to arrive with defibrillators, and if there was someone around who was trained to provide excellent CPR, it increased a person's chance of survival.
"Imagine if no one was there to do CPR, chances are he wouldn't have survived."
Logan said his family had always been close but this episode had brought them closer together.