Wiktionary
adv. expletive used for emphasis after an interrogative word.
Usage examples of "the heck".
Jack pistoned his right fist out, not swinging wildly in the Heck Bast style but driving strong and smooth from the elbow.
For better or for worse, irregular hours were part of the job, even if zapping around the world via radioactive smoke confused the heck out of her body’.
But to a German who has never seen the genuine article, and who's looking through a periscope--what the heck?
Several appeared pregnant, but we didn't see any male equivalents another one of those mysteries, like what the heck they did here, where were they going, and so on.
Ah well, he was on his own, which beat the heck out of taking orders.
But how the heck was I supposed to know Genie was cooking up a deal like that?
It seems you're never able to fight at long range, but what the heck.