The caller, known only as Terry, was taking part in a debate on Liverpool's Magic FM 1548 when the line suddenly went silent. The DJ, Pete Price, was so concerned he abandoned his show and raced around to the man's house.
He said: "It was awful, when I got there the ambulance was already outside his house. Apparently he was found in his chair with the phone by his side. I was flabbergasted. Terry was a regular caller to the show and I knew something was wrong when the line went silent, I just had a gut instinct.
"He told me before the show that he was looking forward to taking part in the phone-in so I'm just glad he died doing something he enjoyed. We all heard his last words."
The drama unfolded shortly after 10.30 on Thursday night as Terry and two other callers took part in the open debate show. When the line went dead the show's producer called the police but was told it was not a priority matter. So Mr Price took matters into his own hands and appealed to his listeners for help. A neighbour, who was listening to the show, broke into Terry's house in the Old Swan area of Liverpool and found him dead in a chair. It is thought he suffered a heart attack.
Meanwhile Mr Price had tracked down Terry's address from one of his listeners and abandoned his studio to race around to the house to help.
He said: "I was very concerned for Terry and just wanted to do what I could, it seemed the right thing to do, to leave the show and try to help."