A novel that runs past nineteen hours is making a promise about depth. Heartbeats is that kind of book, and T.B. Markinson tells it without hurrying, which is the only way a story of this length holds together.
The catalogue files it plainly under LGBTQ+ fiction, and the title supplies the rest: this is writing about attachment, its cost and its persistence. The length allows for the slow accumulation of small moments that gives a relationship on the page its weight, and for the sort of secondary characters a shorter book would have to sacrifice.