/heart must open Heart Core (after reload if you only flipped the module in Settings).

Players
Permission:
smply.heart.withdraw (default true).
Defaults after the Lifesteal preset
heart.yml (excerpt)
Staff
smply.heart.admin. Clears a death ban and restores hearts. Also available from the admin desk.
HUD
The Lifesteal blueprint is hearts-first (no$ on the sidebar). Tokens: {hearts} in hud.yml, %smply_hearts% for TAB. Lines that mention hearts hide when the module is off.
Leaderboards
/leaderboards includes a hearts category when the module is on. Empty boards show a named plaque plus Back, not a blank barrier chest.