A jogger who suffered a cardiac arrest in London's Hyde Park says he was saved after Hollywood legend Dustin Hoffman called an ambulance and waited with him for paramedics to arrive.

The Oscar-winning US actor, who owns a house in the British capital, was passing by when Sam Dempster collapsed while running in the park on April 27, he wrote on his blog.

"A big thank you... to my new found favourite celebrity Dustin Hoffman who called 999 and waited by my side until paramedics arrived," the 27-year-old wrote.

Paramedics told The Sun newspaper that Hoffman, 74, had watched "fascinated" as they restarted Dempster's heart with electric shocks from defibrillator pads.

"He seemed impressed we'd got this guy back so quickly," paramedic Martin Macarthur said in Tuesday's edition of the tabloid.

"When we were carrying the patient into the ambulance he walked up and said 'Great job, guys.'"

Dempster blogged on Tuesday that he was "back home and on the road to recovery", adding that he hoped to be running again soon.

A friend added on the website: "It is understood that the paramedic crew... accidentally packed up Dustin Hoffman's iPod, sunglasses and other possessions in the excitement of loading Sam in to the ambulance."

"We hope these items have found themselves back in your hands Mr Hoffman!"