A Tell-Tale Heart

This story kept me interested.  It was interesting how it was told from the perspective of the so called "not mad" woman.  I think she was deffiinatly "mad".  I would have given her the benefit of the doubt until she started hearing the heart beating under the floor boards at the end of the story.  The way she described the eye of the old man kind of made me want to kill him too.  Is that the sole reason she killed him?  I wonder if the man suspected she would do something like that to him; especially when she described how scared when he sat up in his bed.