Dustin Hoffman has saved a man who suffered a heart attack while out running.

Sam Dempster was exercising in London's Hyde Park at around 9am one day last month when the incident occurred. Dustin happened to be walking in the park too and immediately called emergency services.

"I want to say thank you to Dustin Hoffman. He saved my life," Sam told British newspaper The Sun.

Dustin, 74, spotted Sam as he fell to the ground. He came to his aid and stayed with him while medics rushed to the scene.

It took 15 minutes for the ambulance crew to get Sam's heart beating again using a defibrillator, with Dustin nearby the whole time.

The Hollywood icon praised the medics' efforts, telling them they'd done a "great job" helping Sam.

"I have no memory of what happened. The paramedics told me I had been saved by Dustin Hoffman. It's unbelievable," Sam explained.

Dustin was on hand to speak to the ambulance crew when they arrived, explained he had spotted Sam looking uneasy on his feet with foam at his mouth. He then fell to the ground, hitting his face as he did so.

"Dustin was fascinated. He seemed impressed we'd got this guy back so quickly," paramedic Martin Macarthur said.

"When we were carrying the patient into the ambulance he walked up and said Great job, guys'. He really appreciated what had happened."