verb/mɛ.tʁə dy bo.m‿o kœʁ/
to gladden (someone's) heart, to to warm the cockles of (someone's) heart, to do (someone's) heart good, to be heart-warming
“Les petites attentions qu'il avait parfois pour Maman me mettait de baume au cœur.” — The small thoughtful acts he sometimes did for Mum were heart-warming.
Synonyms: faire chaud au cœur
Literally, “to put balm to the heart”.