Four codepoints, one picture, and two ways to write it wrong

Technically, this is two emoji wearing one costume. Heart on Fire is a ZWJ sequence — a red heart and a flame joined by an invisible "zero-width joiner" character that tells your device to fuse them into a single burning-heart glyph. On software that doesn't recognise the combination, it falls apart into exactly that: a red heart followed by a flame, side by side. That's the giveaway that you're looking at a composite rather than a single carved symbol.

The imagery is old even if the emoji is not. A heart wreathed in flames echoes the Sacred Heart of Christian art and centuries of love poetry that describe passion as burning, and the emoji leans into that romantic reading: intense desire, a love that is anything but lukewarm.

It reached phones fairly recently, in the 2020–2021 wave of additions, which is worth knowing for a practical reason — on older devices it may not render as intended. If you send it and the recipient sees a heart and a flame as two separate pictures, nothing is broken; their system simply predates the recipe that stitches the two together.