speaking to the reader directly: "Hearken! and observe how healthily—how calmly I can tell you the whole story." We are told to listen to his story, but he continues to lead us on without giving us the clear details for his rationale:

You fancy me mad. Madmen know nothing. But you should have seen me. You should have seen how wisely I proceeded—with what caution—with what foresight—with what dissimulation I went to work!

When he finally does begin to give us details, he does so in a very drawn out process, detailing each night he enters the old man's chambers, which certainly adds to the suspenseful mood. It isn't until the eighth night of stalking his victim that he acts, and even on this night, he is very meticulous in detailing his progress. In fact, he is so patient in his act that a "watch's minute hand move(d) more quickly than did (his)." Standing in the chamber, he keeps "quite still and said nothing. For a whole hour (he) did not move a muscle." The reader is kept on his toes and feels the narrator's contained anxiety, yearning to learn his next move. 

Finally, even when he is visited by the police officers, the narrator keeps us in suspense through the use of dramatic irony. He states, "I smiled,—for what had I to fear? I bade the gentlemen welcome. " He knows what's under the floor boards. We know what's under the floor boards. BUT will the police ever find out???

Poe creates tension in several ways.  First, his use of the first person narrator helps build suspense.  For example, right away our narrator address the reader, "True! -- nervous -- very, very dreadfully nervous I had been and am; but why will you say that I am mad?" Here the reader is drawn right in to the story and its tension.  The reader must decide is the man really mad?  Is he reliable?  What can be believe and what might be lies?  All of these put the reader on edge.

Next, Poe's syntax, or word choice, is another way he creates tension.  It is written as if the narrator is confessing to us.  His uses of repetition and asides again draws the reader in and helps build suspense.

Poe also uses plot structure to create tension.  Look at the scene where our narrator spies on the old man at night.  Our narrator slowly opens the door a crack and each night after a little farther until the light falls on the man's face.  Then when he finally is about to enter, after the eighth night, the man wakes up and startles our narrator.  What tension!

Also, look at the methodical nature with which the narrator goes about covering up his crime.  That builds tension. 

Finally, look at the narrator's arrogance.  How he seats himself right over the old man's body buried in his floor boards.  The reader cannot help but wonder will he get away with it?  Will he crack?  Is he insane?  What will happen?

Poe creates suspense by drawing out the telling of this tale and through the use of several symbols that foreshadow the old man's impending death.  

The narrator spends a great deal of time explaining his seven-night routine, how long it took him to open the old man's door, how long it took him to put his head through the door, how slowly he would move so that "A watch's minute hand moves more quickly than did [his]."  He prolongs the account of how he would spend this time, providing a great deal of detail and repetition, in order to create more suspense.  Even the description of what the narrator believes to be the old man's heartbeat, both before he kills the old man and when he believes it to be beating underneath the floorboards, takes a very long time and is likewise repetitive.

In addition, the narrator repeats multiple times that he would perform these actions at midnight, "every night just at midnight."  Midnight, as the narrator says, is the "dead hour of the night."  It signals the death of the day and so often symbolizes death in general.  Likewise, the narrator describes the old man's eye as a "vulture eye"; since vultures are associated with death, the old man's filmy eye becomes connected to death not just because of his age (and cataracts) but because the narrator connects it to this particular bird as well.  These symbols combine to foreshadow the old man's impending death and create suspense for the reader.

Edgar Allan Poe is renowned for his dark and twisted tales. Readers familiar with his works expect the text to be filled with madness, murder, and the supernatural. His texts, therefore, are filled with tension--for both the characters and the readers.

In regards to "The Tell-Tale Heart," tension exists for a couple of reasons. First, the narrator is utterly unreliable. The narrator opens with nervousness about his story. Immediately, he asks his listener (probably a doctor) about thinking him mad. This conflict creates tension between the reader and the narrator based on the fact of the suspicion of his madness.

Secondly, tension is created based upon the unrealistic idea of hating an eye. Readers tend to question the narrator's hatred of the old man's eye and the lengths the narrator goes to in order to rid himself of it. For readers, the idea of murdering over an eye is mad. Some may question why the narrator looks upon the eye every night given his hatred of it.

Regardless of how tension is built, readers agree that tension fills the story. From the nightly visits to the old man's room, to the actual murder and burying of the old man, the narrator's own tension fills the reader with tension.

One of the literary tools that Poe employs to create tension in "The Tell-Tale Heart" is dramatic irony.  A neighbor calls the police stating that a shriek came from the house in the middle of the night.  The narrator has already revealed to the reader that the shriek came from the old man when the narrator was in the process of killing him, but obviously no one else knows the cause of the shriek.  Tension begins to build as the reader wonders whether or not the police will find out about the narrator's crime.  When the narrator then takes the drastic step of parading the police around the house and then inviting them to sit over the very spot where the old man is buried, the tension is high because the reader is privy to what lies right beneath the police while the police are entirely unaware and unsuspecting because they have not seen anything amiss in the house.  So, dramatic irony in the story causes the reader who is knowledgeable about occurrences in the story to feel the tension and suspense in the possible discovery of the narrator's crime.

In Edgar Allan Poe's short story "The Tell-Tale Heart," he creates a tension in the story that the readers can actually feel. There is a heightened level of suspicion that sets readers on edge as they try to figure out whether the narrator is insane or sane. Poe accomplishes this by several techniques. One is the narrator's voice. The narrator is very emotional and seems highly excited. Poe includes lots of short phrases and uses exclamation marks to show this.

Another technique Poe uses is the heart beat. The narrator claims he hears a heart beat throughout the story and this beating sound is easily imagined by the reader, adding to the tension. One more technique is the narrator's direct address of the reader. By addressing "you" throughout the story, the narrator draws us in as if he is telling us the story directly. All of these techniques are efforts on the author's part to make the readers feel suspense and terror as they read on.

The answer below is really well put. I would like to add that Poe uses such thoughtful imagery and really appeals to his reader's senses in this story that we can almost hear the beating of the heart beneath the floor boards as the story is unfolding. Poe so closely connects us with his narrator and characters that we feel the suspense that it being felt in the story. We know that the end is getting closer, we go crazy as the character goes crazy. Poe's use of imagery and repetition in this story is what keeps us engaged until the confession!

Ahhh...Poe is the master of suspense.  From the opening lines, the reader has a sense of foreboding.  S/he knows the old man is in danger and completely clueless as to the narrator's animosity towards him.  As the narrator describes his vigil waiting for the old man to finally slumber, our apprehension grows.  Even when he finally does the horrific deed, we are shocked by its senselessness and brutality. 

As with many of Poe's tales, there is no logical explanation for the unfolding of events, a fact with which the rational mind struggles; a fact which increases the horror of inexplicable inhumanity. 

Two ways that Poe creates tension that are not mentioned in the first response are the uses of foreshadowing and irony.

The narrator foreshadows that the old man’s heartbeat will lead to the narrator’s exposure to the police. On the night the narrator says he killed the old man, he remembers hearing “a low, dull, quick sound, such as a watch makes when enveloped in cotton,” which was the old man’s heartbeat. This creates tension because it shows that the narrator is hyper-focused on and disturbed by specific sounds.

However, the most effective technique that creates tension is the use of dramatic irony. Because the narrator tells the reader that he hid the old man’s body beneath the floorboards, the reader experiences heightened tension when the police sit atop those same floorboards. Since the reader knows what the police do not, the reader anticipates some type of conflict. Of course, this is exactly what happens: the narrator’s guilt compels him to reveal his secret.

Poe creates tension using a number of techniques. One is the rhythm of the dialogue. The narrator says, "‘True!—nervous—very, very nervous I had been and am; but why will you say that I am mad?’’ The very pattern of interrupting himself creates tension from the first line.

Second, he does so by setting up specific claims and expectations. Why is the narrator nervous—and why would the listener think he's crazy? Unanswered questions like these create tension.

Third, the story's tight focus on the old man creates tension, as does a fourth point: the search by the authorities. There's a lot of threat there.