The Hep Cat opens with a cat (claimed by some to be a prototypical version of Sylvester the cat) strolling through an abandoned lot. Unfortunately, he stumbles across a dog named Rosebud"—otherwise known by fans as Willoughby the Dog—who, upon noticing the cat, gives chase. The cat, after a successful escape, begins singing "Java Jive." Later, the cat encounters an attractive female cat, and attempts to woo her, failing utterly. Suddenly, Rosebud the dog reappears and the chase resumes. After a series of zany, Clampett-esque sight gags, the cat once again evades the dog. As the cartoon closes, the cat can be seen kissing his dream girl—a puppet.
When Cartoon Network aired this short on The Bob Clampett Show, the titles were replaced with title cards of a colorized Porky Pig Looney Tune, with The Merry-Go-Round Broke Down as the opening music. The Looney Tunes title card cuts to the Blue Ribbon title card with Merrily We Roll Along as title music. The Looney Tunes drum with Porky Pig saying That's All Folks!, also closes the cartoon. This was done to identify the short as a Looney Tune, since the Blue Ribbon titles miscredited the short as a Merrie Melody.
The opening title cards are not correct, since the 1942-43 season was the first in which Looney Tunes cartoons opened with the "bulls-eye" titles, usually with thicker rings.
When the cat claims to be a "gorgeous hunk of man" his face turns into a caricature of Victor Mature. As the cat feels Willoughby's hand beside the puppet he's kissing he exclaims: "Ah, something new has been added!". At the end of the cartoon the cat says: "Well, I can dream, can't I?" Both quotes were used often in Looney Tunes cartoons of this era (like for instance Plane Daffy, Red Hot Riding Hood,...) and are both catch phrases by Jerry Colonna. "Ah, something new has been added" was a slogan for Old Gold (cigarette).