One could only assume what "unnoticed thoughts/ideas" exist within Mary Shelley's novel Frankenstein. Given that these thoughts and ideas are not blatantly stated, the only way to define the thoughts of Victor or his creature is through subjective thought.
Victor is very blatant about his feelings regarding his studies, his creature and his feelings for his family. Outside of that, it seems that every time something horrible happens to him (the death of his brother, the death of Henry, and the coming to life of the creature), Victor lapses into illness. It would seem that his guilt manifests physically.
Therefore, one could justify that Frankenstein's heart is contaminated based upon the fact that his obsession with reanimating life is only superficial. It is through Victor's obsessive actions (ignoring his family, shutting himself in his laboratory, and isolating himself from humanity) that his contaminated heart is able to be noticed.
Therefore, Victor's "contaminated heart" is a result of his obsession. He is unable to look at the things around him for what they are really worth. Elizabeth's love, while Victor is experimenting, does not matter. Victor's family, namely his father and his health, do not matter. Victor's own health does not matter. The only thing which matters is the success of his experiments, nothing more.