Conversation so far:
What did Lowell Thomas do?
Thomas's most amusing on-air gaffe.
What is this?
He was reading a story "cold" (going on the air without pre-reading his copy, contrary to his usual practice.
WHat did he say?
She suffered a near fatal heart attack".
The line came out of Thomas's mouth as.
What actually came out of his mouth?
line came out of Thomas's mouth as "She suffered a near fart ...
err fatal heart attack".
What did he do?
Realizing instantly what he had said, he tried to continue.
What happened?
eventually collapsed into gales of laughter, which continued into - and beyond - his announcer's chuckling sign-off for the day.
Who helped him?
Thomas' long-time friend and ghostwriter Prosper Buranelli wrote the nightly newscasts.
What did he send him?
day's script was sent by teletype to Thomas' home in Pawling, NY.
Where did he work from?
One evening, Buranelli's final story was about an actress going into a Los Angeles hotel with a Great Dane.

Question: What was the joke?
Self-contained rewrite: What was the joke that Buranelli made?