There is some evidence that Montresor felt a small amount of remorse after he killed Fortunato.
Montresor is not a mentally stable man. We can tell this because we know that Fortunato insulted him in some minor way that was so insignificant that Fortunato himself was not aware of it (or he never would have gone into the catacombs with him at night, letting his guard down), and yet he still wants to kill him. Montresor is a murderer. He wants to kill this man, and plans a cold-blooded murderer in such a way that he can get away with it. This is of utmost importance to him. If he doesn’t get away with the murder, he will not have gotten his revenge.
At first, we know that Montresor has felt no remorse. He seems to luxuriate in the murder, stopping several times to enjoy Fortunato’s suffering.
… I heard the furious vibrations of the chain. 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.
It certainly seems as if he is enjoying the fact that his victim is frightened out of his mind. He stops to enjoy it. He waits it out, sitting on a pile of bones. It definitely seems to be the work of a disturbed, demented, remorseless, despicable mind.
However, if you look closely, you will also notice something else. You will notice that Montresor is not as self-assured as he seems. He seems confident. He has planned every detail. He has everything prepared, he convinces Fortunato to come down, and he uses reverse psychology beautifully. He seems every bit the megalomaniac. Yet while he talks about his family crest, says he is a connoisseur of wine, and pretends to be a Mason, it is clear that he not the member of that secret society. This calls into question the other things too. Perhaps he is just a pretender, and not as self-confident as he pretends to be.
Notice that after his play of strength, sitting on the bones, the shrill of the screams causes him to thrust “violently back” and even tremble. That could definitely be a sign of remorse.
However, the greatest indication that Montresor actually does have some remorse is what he says himself, when he finally realizes that he has killed a man.
No answer still. I thrust a torch through the remaining aperture and let it fall within. There came forth in return only a jingling of the bells. My heart grew sick; it was the dampness of the catacombs that made it so.
He dismisses the idea of remorse, but that does not mean he did not feel it. He wants to be this cold, hard, murderer. He wants to get revenge. Yet at the same time, he did feel sick. He dismisses it as the dampness, but it wasn’t. It was regret. It was the realization that he did kill someone. It was remorse, plain and simple. It might have been a tiny bit of barely acknowledged remorse, but it was remorse nonetheless.