The region of the heart is a luminous space, pulsing a pleasing cadence. Usually.
But here is let in inky fumes of red-black substance! Blinding, spreading haze. The creature darts in frantic evasion but the discoloration grows. Diffuses and grows till it gathers you up in its swirl. Rest quiet, if you can; do not flap about: a limp acquiescence may save you yet. But you won't, of course.
Once the black storm is done, you clean house. Pump in fresh goodness by way of sweet breath. Or by expelling the poison from the pores. But waiting is good – the muck leaches out eventually, leaving, if you’re lucky, no trace. The shrine is pleasant once more. Only, a little wary.