[3][4] The album was recorded at Attica Studios in County Donegal and was self-produced, with the band stating that "they wanted Heart Under to feel like the experience of driving through a tunnel with the windows down".

[5] Poppie Platt of The Daily Telegraph, also found Heart Under to be a departure from the group's shoegaze sound, describing it as "moody and dark, with industrial guitars and no typical choruses", in a five-star review.

[8] Max Freedman of Paste labelled the album as "a tornado of distorted dissonance", and claimed that it "places them among the vanguard of the British Isles' ever-crowded post-punk scene".

[13] Robin Murray, writing for Clash, described Heart Under as a "striking, fantastically original work that taps into animalistic emotion",[7] whilst Siobhán Kane wrote in The Irish Times that it "speaks to power of resilience".

[11] Writing for The Line of Best Fit, Kyle Kohner claimed that though "the decidedly blue atmosphere of Heart Under can be a bit one-note, albeit seldomly, it still frequently froths from lips, almost unceasingly, with the type of music you wish more post-punk revivalists, bedroom pop darlings, and even some shoegaze traditionalists would aspire to make more of".