The most prominent theme in The Facts in the Case of M. Valdemar is that no one can escape death and that interfering with the process of dying can be very dangerous and impose unforeseen consequences. In this story, Poe uses words and phrases with dark connotations to convey a somber tone throughout the passage. In addition, the imagery that Poe creates imparts a gloomy feeling so the reader can infer that something bad will happen in the story. The argument could also be made that the descriptions and choice of words in the story continue to get more and more horrific as the story goes on, which represents the deterioration of Valdemar.

The way Poe describes Valdemar throughout the story can help explain how the story proceeds from just somber and gloomy, to downright horror. Before Valdemar is put in a mesmeric trance at the moment prior to death, Poe describes his condition: "His face wore a leaden hue; the eyes were utterly lusterless; and the emaciation was so extreme, that the skin had been broken through by the cheek-bones. His expectoration was excessive. The pulse was barely perceptible" (Poe 14). The way Poe describes Valdemar at this point in the story presents a clue as to how gruesome Valdemar will look at the end of the story, especially if one is familiar with Poe's techniques. If the reader pays close attention, he or she will notice the constant downward spiral in which Poe describes Valdemar's condition. On the next day, just moments before he is put into a trance, his condition has deteriorated even further and the author describes him again: "By this time his pulse was imperceptible and his breathing was stertorious, and at intervals of half a minute". (16)  Poe now describes Valdemar's condition as worsening, and he exists merely inches from death. The consequences, both to Valdemar and the living, of delaying him from death explains itself at the end of the story.

While in a mesmeric trance, Valdemar could still communicate when commanded by the man referred to as P., but when he wasn't being experimented on he appeared dead, but he couldn't die in the mesmeric trance. When doctors and physicians, and in this case mesmerists, experiment and try to control the circumstances which determine whether someone lives or dies, there is a lot of potential for things to go wrong. For example, when someone is put down because they have received the death penalty or are being euthanized sometimes errors can occur. The patient may go through an extreme amount of pain and could be on the brink of death for far too long. In a similar way, Valdemar is on the brink of death for seven months in this story while in a mesmeric trance. Finally, after seven months of being kept responsive to P.'s commands, Valdemar was awakened. "His whole frame at once-within the space of a single minute, or even less, shrunk-crumbled- absolutely rotted away beneath my hands. Upon the bed, before that whole company, there lay a nearly liquid mass of loathsome- of detestable putrescence". (19) This last quote basically summarizes the prominent theme in the story: one shouldn't experiment with death and try to prolong it unless you are prepared to face the consequences. In this case, the body actually had died and was in the process of decay.  Having been mesmerized, Valdemar only appeared to continue to live, even making sounds with a quivering tongue, but in reality it was only the effect of the mesmerization that people witnessed, an illusion, not the real thing. At the beginning of the story, P. wonders whether the experiment would prolong the life span of the individual being mesmerized, he probably thinks that it did, but all mesmerizing did to Valdemar was cause his death to be too long, seven months too long, and much worse than it should've been had he been left alone to die in peace.  

One of the things that contribute to the overall horror of the story is some of the word choices that Poe used, as this also ties back into the fact that the mood of the story gradually starts to become darker and darker as the story continues to go on. The descriptive terms he uses at the end of the story are much more horrific than the words that he uses at the beginning. For example, at the beginning of the story P. describes the situation as an "unpleasant representation" (13) while at the end of the story he describes Valdemar's remains as "detestable putrescence" (19). The first word choice is not as gloomy or death-ridden as the one at the end.  This comparison represents the constant deterioration and slow death of Valdemar. None of the words or phrases used by the author in this passage have any additional or hidden connotations that might affect the themes of the passage. Everything was straightforward and the story continued to challenge the imagination and continue to be more and more terrifying until, at last, the reader realizes that tempting fate is a dangerous effort.

This story specifically deals with the theme of impending death and how people can try to stop it, slow it down, and tamper with it, which often causes very bad, horrific situations. The reader is placed in the position of becoming more and more involved, wondering how it all will end, meanwhile having to suffer while imagining the horror that awaits those who will witness the conclusion.
