Dustin Hoffman was there to save the day, while he was walking in a park near his home in Kensington when a 27-year-old jogger suffered a heart attack nearby.
The 'Rain Man' star reportedly witnessed the man collapse, hitting his face hard on the ground as he fell. Hoffman stopped to help him and phoned emergency services.
Hoffman, 74, stood by as paramedics performed CPR on the jogger, who has been named as Sam Dempster.
The team managed to get Mr Dempster's heart to beat again, saving his life. He was then taken to hospital where he had a device fitted to restart his heart should it stop again, in a similar operation to Bolton Wanderers player Fabrice Muamba, who collapsed during a football match in March.
The lawyer told The Sun: "I have no memory of what happened. The paramedics told me I had been saved by Dustin Hoffman. It's unbelievable.
"I want to say 'Thank you' to Dustin Hoffman. He saved my life."
Hoffman told paramedics that Mr Dempster had been frothing at the mouth and staggering.
The actor was thoroughly impressed by the skill of the medics, telling them "Great job, guys".
Paramedics, Martin Macarthur and Luke Sullivan, restarted his heart with defibrillator pads as Hoffman looked on. Mr Macarthur, 45, said: "Dustin was fascinated. He seemed impressed we'd got this guy back so quickly.
"When we were carrying the patient into the ambulance he walked up and said 'Great job, guys'. He really appreciated what had happened."
Mr Dempster applauded Hoffman and the paramedics on his recovery blog "Heart-throbbing". He wrote:
"A big thank you also to my new found favourite celebrity Dustin Hoffman who called 999 and waited by my side until paramedics arrived and the staff at the Chelsea and Westminster Hospital that stabilised me before I was transferred to the Royal Brompton Hospital."
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