While the party is stranded on a boat in a marsh, Victor complains that they've wound up on the set of Apocalypse Now (1979). That movie was based on the novel Heart of Darkness, from which the title of this episode is derived.
Scenes which included an elderly man being physically abused by staff, an elderly woman and an elderly man being locked in the cupboard under the stairs was temporarily cut out in subsequent re-runs, after its first broadcast after it attracted several complaints. The cuts have since been restored, along with them being available in the box sets.