Roundabout's first new Off-Broadway musical in years follows a single donor heart through the 24 hours after a young surfer's death, tracing the two families and the medical team bound together by one transplant. Christopher Ashley, the company's new artistic director, directs a score by Anne and Ian Eisendrath (of KPop Demon Hunters) and a book by Kait Kerrigan, adapted from Maylis de Kerangal's novel Réparer les vivants. It runs at the Laura Pels through December 6.