David Walker, 69, had just completed the 5km parkrun in 21 minutes and was collecting his finishing token when he collapsed.
The Battersea parkrun volunteer team quickly ran to help, with someone taking the parkrun’s defibrillator.
Dr Stephen Murphy, an off-duty doctor who had also done the run, was nearby and also offered assistance.
David, a former computer scientist at Cardiff University, came to London from Cardiff earlier that day to meet his daughter Katherine and take part in the parkrun.
He said: “I was waiting to collect my token and I felt dizzy.
“The next thing I remember I was on the floor waking up with lots of people standing around me.
“I had been revived following a shock from the defibrillator.”
London Ambulance Service paramedics arrived within four minutes and took David to St Thomas’ Hospital where he had surgery for an implantable cardioverter defibrillator – a small device that corrects irregular heartbeats.
David’s daughter Katherine said: “I was alarmed when I picked up a call from my dad and it was the police telling me he had a cardiac arrest.
“I was expecting the worst when I arrived at A&E, but I was relieved to find he was awake and oriented.”
Last year, ‘Life Hikers’ at Battersea Park raised almost £25,000 – enough to pay for 15 defibrillators.
Mark Faulkner, consultant paramedic and associate clinical director at London Ambulance Service, said: “It’s incredibly important that bystanders start CPR and use a defibrillator as quickly as possible.
“These two things are really easy to do and more than double a person’s chance of surviving a cardiac arrest.”
David added: “I’m very grateful to everyone who was involved in saving my life.
“I don’t think I’d be here without them.”
Dr Stephen Murphy, a critical care doctor at Guy’s and St Thomas’ NHS Foundation Trust, said: “I was thrilled to hear that David has made a full recovery.
“This type of event shows the life-saving impact of early CPR and how it can provide the best chance of survival for anyone having a cardiac arrest.”
