Throughout most of his evil deed against Fortunado, Montresor does not demonstrate any sense of guilt or regret. In fact, he seems to be rather enjoying himself and his diabolical plan. He teases Fortunado along, goading him and very cleverly manipulating the man to go further and further into the catacombs. At one point, when Fortunado is screaming and struggling with the chains, Montresor states,
"The noise lasted for several minutes, during which, that I might hearken to it with the more satisfaction, I ceased my labours and sat down upon the bones."
So not only is he enjoying the screaming, but he sits down to relish it even more.
There is one point however, that Montresor shows a bit of hesitancy. Guilt? Not sure, but hesitancy for certain. Fortunado picks up the pace of his screaming, and Montresor writes,
"For a brief moment I hesitated, I trembled. Unsheathing my rapier, I began to grope with it about the recess"
So, he is a bit worried and startled; he sticks his sword in to try to determine if Fortunado is still standing, or get a sense for what is going on. He hesitates in his plan. However, his hesitation lasted for merely "an instant" before he resumed his work with great satisfaction.
The best indication of guilt is at the end. Fortunado has stopped making noises, and is silent. Montresor writes, "My heart grew sick". The thought of Fortunado dying in there, for a moment, makes him sick. However, he blames it on "the dampness of the catacombs" and hurries away. So, his sick heart does make him feel bad probably, but in denial, he blames it on something else and rushed away. The fact that he is confessing his story at a later date might also indicate that he has felt guilty for it, because he is unburdening himself of the tale.
I hope those thoughts help; good luck!
In Gothic narratives such as Poe's "A Cask of Amontillado," the narrator has the "privilege of irrationality and passion over rationality and reason" (enotes). That being stated, it is, indeed, questionable that Montesor feels any guilt whatsoever over his murder of Fortunato. That this murder is premeditated is apparent from the beginning of the story as Montesor mentions that he has borne "a thousand injuries," but now has finally vowed revenge and has a singleness of purpose, so typical of Poe's narrators.
Like a cat who toys with his victim before finally killing it, Montesor leads the unwitting Fortunato through narrow, damp openings in the catacombs, parodying him with mock gestures of a mason as he puns on the word itself, feigning concern for his welfare, only to take him farther until finally tethering his unsuspecting victim to a wall. When Fortunato screams, Montesor hesitates as a cat hesitates to see so much life left in his victim. He pulls his sword, not out of any guilt, but to reassure himself that there is no escape for Fortunato.
In the final paragraph the irrational narrator wishes to still hear agony in his victim. He "thrusts a torch through the remaining aperture," but a "jingling of bells" is the only response. "My heart grew sick--on account of the dampness of the catacombs," Montesor says, and he hastens to make an end of his work. Like the cat who is disappointed that his prey is now limp and no more fun to torture, he leaves the scene. Certainly there is no guilt in the narrator's subsequent remark, proudly and mockingly said,
JFor the half of a century no mortal has disturbed them. In pace requiescat!