It’s for the best that Jonathan Cuartas wastes little time delving into the past of the trio of siblings at the center of “My Heart Can’t Beat Unless You Tell It To,” a family drama that hides underneath a cloak of horror. The film may feature characters that are out for blood quite literally, when siblings Dwight (Patrick Fugit) and Jessie (Ingrid Sophie Schram) are obliged to take care of their sickly younger brother Thomas (Owen Campbell), who thirsts for the red stuff, but the writer/director is after something more with his debut feature, watching as the task of keeping Thomas’ energy up drains Dwight and Jessie of theirs, leading to a breaking point between the brother and sister who may be able to keep Thomas alive with their ongoing arrangement, but likely won’t survive it themselves.

Why Jesse and Dwight don’t have the same thirst as Thomas is never explicitly addressed in “My Heart Can’t Beat Unless You Tell It To,” but Cuartas is wise to leave it alone, preferring to concentrate on the resentment that builds between the siblings than give any air to tortured exposition that might cut the tension. As Thomas struggles to barely get out of bed, Jessie works at a local diner to keep a roof over their head while Dwight is charged with bringing home fresh blood, an onus that seems increasingly unfair relative to his sister’s responsibilities when he’s driven to more and more dangerous measures to maintain their supply. Already desperate to leave, he is sent over the edge by Jessie’s suggestion to put a local prostitute (Katie Preston) in his crosshairs, unwittingly tearing him apart with her feeling that no one will miss her when his clandestine visits to her have become his only respite.

Told within the confines of a tight square frame, the early claustrophobia of the film gives way to a voyeuristic remove as the family grows apart from each other and see themselves individually moving away from any humanity they may have had, acutely observed through Michael Cuartas’ unforgiving lens, but also revealed with great skill through Fugit’s nuanced turn as Dwight, whose burden grows to feel as heavy as the shadows he’s constantly surrounded by. (With brothers Rodrigo and Michael in charge of the production design and cinematography, respectively, there is something darkly amusing about one clan building a haunted house for another.)

Running a lean 89 minutes, “My Heart Can’t Beat Unless You Tell It To” shares a brutal efficiency with the siblings onscreen, only occasionally lingering on strange moments inside the family to show how even if they were able to break free of their commitments to one another, they might not fare well on the outside. Oxygen may feel as if it’s at a minimum in the world that Cuartas has created, but the itself feels like a breath of fresh air with its sharp execution, knowing that in this day and age it’s more satisfying to have something to sink your teeth into than watching others do it.

“My Heart Can’t Beat Unless You Tell It To” does not yet have U.S. distribution.