Hearing a funny noise, she thought "that's not right".
Finding Steve unresponsive at the breakfast bar, she shook him.
"Your body wants to panic, but you have to tell it not to and just do what you need to do."
Cellphone reception was limited on the couple's rural lifestyle block, so she dialled 111 on the landline.
"The 111 call taker was absolutely brilliant at keeping me focused."
"I knew I needed to do CPR – my mum was a nurse and taught me a lot – but it was 20 years ago, and things have changed."
The call taker gave instructions on what to do.
After 20 minutes of CPR, the paramedics arrived.
"It was tiring, but I just had to keep going."
When the ambulance left, Steve had a 50/50 chance of survival.
He was flown to Wellington Hospital where he spent two days in an induced coma.
Two weeks later, he was fitted with a pacemaker defibrillator and returned home.
Steve doesn't remember much from that day but knows he is fortunate to still be alive.
His perspective on life has changed: "I try not to stress about the small stuff now".
The couple now regularly donate to Wellington Free Ambulance; it's their way of saying thanks.
"There are a lot of people who worked together to save my life and to get me to where I am today."
"I have a lot of guardian angels; there's one sitting beside me and others I don't even know."
He and Diane encourage everyone to learn CPR, especially their rural community.
They undertook Wellington Free Ambulance's Heartbeat training programme that teaches lifesaving CPR skills to the community for free thanks to the Lloyd Morrison Foundation.
Diane wanted a refresher; Steve wanted to help her, if ever needed, as she had done for him.
Wellington Free Ambulance's Wairarapa Heartbeat co-ordinator Matt Hitchiner said: "In rural areas, medical help can take time to arrive, and every minute without CPR, the chance of survival decreases by about 10 per cent."
"Through Heartbeat, we teach compression-only CPR at a rate of 120 compressions per minute.
"That may seem like a lot, but we teach you how to work as a team."