The Rain Man actor was walking through Hyde Park in April (12) when he saw Sam Dempster fall to the ground, and he raced to help the sick man, staying by his side as paramedics carried out cardiopulmonary resuscitation (CPR).
Dempster subsequently thanked the 75 year old in a national newspaper, but the star admits he was shocked the drama made the news because of his involvement.
Recalling the incident, Hoffman tells Britain's Guardian Weekend magazine, "He looks as if he's resting, and then boom! He hits the concrete and his face gets totally bloodied up and I realise something is wrong - his eyes are open, he's dazed, he can barely breathe, and I just happen to be the one there. So I start yelling out: 'Do you have 911 here, what's your equivalent of 911?' and someone comes over and calls it, and I say, 'I don't think you should move him.' He's on his side.
"The paramedics got there within four minutes. It was across the road from the (Royal) Albert Hall. They come running out, they've got the defibrillator, and a portable cardiac thing, they cut open his shirt, they defibrillate him, it's like clockwork. Then I go out to get the papers the next morning and it says I saved somebody's life... I was there! That's all."