Always Hardcore Heart

Hardcore Hearts is a lightweight, client-side Fabric mod that displays hardcore-style health hearts in every Minecraft world, even when the world is not set to Hardcore mode. It does not replace textures or redraw the HUD, so your active resource pack continues to control the exact heart appearance and animations. Install it only on the client; no server installation is required. With Mod Menu installed, you can enable or disable the hardcore heart style from an in-game configuration screen at any time.

This is my first mod, so there may be bugs. Also, since I created it for my own use, updates might be infrequent.