Sweet Magos Biologis.
I wonder if he's Adeptus or Dark Mechanicus? That seems to be a mutant/cultist he's operating on, and the man is not well restrained.
Well, all those things could be off-panel! We don't know!
And I'd always assumed the DarkMech had swapped most of their holy chants for "Fuck Mars, seriously, screw those guys, who needs them".
I wasn't referring to Hereteks in general, but Dark Mechanicus specifically. The Dark Mechanicus is limited to the rebel branch that was essentially dragged along with the Chaos Space Marines to keep all their gear running in the giant pit of unreality where they live (and boy, those guys must have it rough). Although I'm sure even the DarkMech has numerous different sects and sub-cults depending on what Legion they're most closely aligned with, Chaotic leaders they've fallen in with, and random acts of Warp-muckery that might have influenced their teachings.
I'm pretty sure hating Mars and the Loyalists who absurdly claim the Emperor is the Omnissiah is a requirement to join up with the Dark Mechanicus.
Of course, there are countless other "Hereteks" who would be ordinary Techpriests but for some political foible or minor dispute with Martian dogma - it's a pretty big galaxy - but most of those wouldn't be caught dead stitching up a Chaos cultist.