"I did 12 minutes on the treadmill and collapsed four minutes 20 seconds into recovery ... a cardiac arrest," he said.
"They said at the time it was ventricular tachycardia. My left descending artery in my ticker was 99 per cent blocked and my heart couldn't pump the blood through fast enough.
"It seems the blood backs up, your blood pressure drops ... and so did I. Usually it means you're dead but somehow my ticker rejigged itself without needing an electric shock."
He learned later his heart had "flat-lined", and a cardiac surgeon told him the incident had been life-threatening and he was "very lucky indeed".
After five days in Christchurch Hospital he got out on Good Friday with a stent in the previously blocked artery.
Six weeks later, Sumner had "another funny turn".
"I was in the car, with my wife Jude driving. I'd done nothing too strenuous when all of a sudden I felt real bad."
He felt himself collapsing but stayed conscious as Jude got him to hospital. He was admitted and "felt lousy" for about three hours.
The next day he did another treadmill test. In 13 minutes 54 seconds his heart got up to 158 beats a minute, and the angiogram showed the stent was in good shape and other arteries were OK.
"They decided the electrics in my heart might need some help so they put a defibrillator in. It won't stop me having a cardiac arrest again but it will prevent me from karking it if I do have one. It will also double as a pacemaker, should I need one."
Sumner said the doctors told him his fitness probably saved him.
"I'm in pretty good nick for 57. I was training twice a day, every day, on the bike and in the gym. But little did I know that my artery was so blocked that they think it was probably only my fitness that saved me.
"It's funny ... at the gym over the past month I've seen blokes our age busting a gut thinking they are doing themselves good, but how many know they might have a ticking time bomb in their chest. I don't know what the answer is, but get checked out.
"How many times do we hear so-and-so died while playing squash, riding a bike, playing football, going for a run. Please take care."
From 1976 to 1988, Sumner played a record 105 times for New Zealand, scoring 27 goals, including a national record six against Fiji in the 1981-82 World Cup qualifying campaign. He captained the All Whites throughout that campaign and at the finals tournament in Spain.
Sumner won six Chatham Cup winners' medals - more than anyone else. Four of those came with Christchurch United, one with Manurewa and one with Gisborne City, for whom he was player-coach in 1987. He won four National League winners' medals at Christchurch United and one at Manurewa.
He coached Gisborne City to second place in the league.
Steve Sumner made 283 National League appearances in a New Zealand football career interrupted by a two-year spell in Australia.
Born in Preston, Lancashire, Sumner was with English league clubs Blackpool, Preston North End and Grimsby Town before former Irish international Peter Doherty put him in touch with Christchurch United in 1973. It was a fresh start for the 17-year-old midfielder, and one that set him on the path to national and international honours.
Sumner was inducted into the New Zealand Soccer Media Association Hall of Fame in 1991, and into the Sport Canterbury Hall of Fame in 2009.
He was awarded the Centennial FIFA Order of Merit in 2004 and in 2010 he became the first and so far only person in New Zealand to receive FIFA's top award, the FIFA Order of Merit.
