An inventor dies while waiting to see someone at the company that used to employ him. Apparently he has invented a new technique for time travel and wanted to show that his ideas, that the company had fired him for pursuing, were correct.
He was then going to take the design to another company, he was waiting to rub their noses in the situation. Unfortunately he went on a busy day and as he waited he became more and more frustrated until he had a fatal heart attack.
The folder he is carrying has full details of his invention, and the person who he was waiting to see decides to steal the plans. He leaves his job and intends to set up a rival time travel company using them. Possibility: I think the first company could only see into the past and the improvements would enable people to travel there?
I read this in an anthology sometime in the 1970's.