Buddha never taught we had a heart of darkness. Heart of Darkness is a novella by Polish-English novelist Joseph Conrad about a narrated voyage up the Congo River. Why do you think these writings are Buddhist? Copying Christian scripture or Prayers and changing a few words or phrases here or there in no way makes them "Buddhist." Why would a Buddhist be interested in reading mangled Christian scripture and Prayers? Don't Buddhist's have their own scripture?

The sources do not seem to be Buddhist web sites. Just seems to be a random blogger trying to get clicks.