"He was the most horrific blue I've ever seen in my life," Mr Woolford told the Herald.
"He was just completely dead, there was no pulse, no breathing, nothing — so I just gave him CPR."
Ms Woods, who had already called 111, said Mr Woolford's efforts saved her partner's life.
"Sam just leapt over the fence. It was unbelievable. He ran in and he took the phone from me and got me to help move Kevin. He saved his life."
Mr Woolford, who learnt CPR when he worked as a diving instructor, performed CPR for about 10 minutes until ambulance staff arrived at the New Lynn property.
"He had a pulse by the time paramedics turned up," said Mr Woolford. "They got him breathing on his own again — they gave him a huge amount of adrenalin and they shocked him [used a defibrillator] ... three or four times at least."
It took paramedics about 30 minutes to stabilise Mr Walker, who stopped breathing for an estimated 14 minutes. He was transported to Auckland City Hospital where he had triple-bypass surgery and had a defibrillator implanted in his chest.
Mr Walker, who was in an induced coma for three days, described his first encounter with Mr Woolford after his five-week hospital stint as "emotional" — particularly as they'd barely spoken before.
He and Ms Woods moved to their new home only three weeks before his collapse on May 17.
"When you get new neighbours ... you say you'll catch up and have a beer but we didn't catch up and have a beer in the three weeks. There were a few tears [when we met]," Mr Walker said.
The actions of Mr Woolford and his wife Nicci had been "unbelievable".
"If we had a million bucks and gave it to him it would still not be enough to say thanks."
Cardiac arrest
• The heart suddenly and unexpectedly stops beating, preventing blood flow to the brain and other vital organs
• Occurs in about 1500 people each year in NZ
• Low survival rate, between 4 and 12%
• The length of time before life-saving measures is crucial to the patient's survival and neurological outcome
- Source: GreenLane Cardiovascular Service, Auckland City Hospital