This informal exclamation is a less offensive substitute for hell.
Heck, I left my wallet at home.
What the heck happened here?
This use strengthens questions expressing surprise, frustration, or curiosity.
Where the heck are my keys?
How the heck did you solve that?
In the expression a heck of a, the word emphasizes that something is unusually difficult, large, good, or intense.
It was one heck of a journey.
She gave us a heck of a performance.
