Heyerdahl is primarily known for his recurring role as the enigmatic "Swede" in AMC's Hell on Wheels. This post-American Civil War drama debuted as the second highest rated original series in AMC history. He is also known for his role as Leonid in the Are You Afraid of the Dark? episode "The Thirteenth Floor" and as Nosferatu in the episode "Midnight Madness". He played the characters Halling and Wraith commander Todd in Stargate Atlantis, and Pallan in the Stargate SG-1 episode "Revisions". He played H. P. Lovecraft in the film Out of Mind: The Stories of H. P. Lovecraft (1998) and a punk, new at drug dealing, in Cadavres (2009).