John Stirling, 59, was cutting branches off a tree in his garden in Peacehaven, East Sussex, when he is apparently slipped and cut off his left arm.
He then calmly walked to the home of his neighbour Steve Francis and knocked on the door and said to him: "Please help, I've cut off my arm."
Francis said that he "wasn't screaming" and appeared "as relaxed as can be" despite the blood flowing out from his wound.
"I didn't realise anything was wrong until I looked down and saw his arm was missing," Telegraph quoted Francis, as saying.
"I ran inside to call the ambulance and he sat outside on a stool. I came out and tied his arm up with a belt and towels.
"The ambulance people talked me through it. But through it all he sat there talking away like it was normal. He's a brave man, I'll give him that. I couldn't believe he didn't faint," he added.
While the paramedics examined Stirling, Francis put the severed arm in a plastic bag and added frozen snacks from his freezer to keep it cold and handed it over to them.
Stirling underwent a marathon operation to reattach his limb and is now recovering from the surgery at Queen Victoria Hospital in East Grinstead.
"He is doing very well and is comfortable after what was very complicated surgery and took 14-hours to complete," said a hospital spokesman.
"The procedure to reattach his arm went very well and the medical team are pleased with the patient but it is still early days to say if the operation is a complete success," he added.