what does the title relate to the swtting of heart of darkness? what does this comparison suggest to you about the themes of the text?

Just to make sure, do you mean "setting"?

The heart of darkness takes place along the Congo River. At this time, it was pretty much uncharted territory. Here the white "pilgrims" and colonizers lost themselves in the sweltering mythic chaos of the jungle. This was a place where the heart of darkness was, where guys like Kurtz lost their minds in the darkness of "savagery". Still there is another larger theme. The setting ironically begins to personify the hearts of the white people themselves. More than the darkness of the jungle, the evil within the hearts of Europeans eclipses any mythic darkness in the jungle.