Answer: indecisive about killing the old man.
At this point in the story, the narrator is about to kill the old man. He has opened the door and is staring right into the old man's eye. He realizes the man must be really scared, as his heart was beating very loudly. The sound of the man's heart made him nervous, and he struggled to carry out what he had planned. This shows that at that moment, he was indecisive about killing the old man.