IPA: /ˈdaʊnˌhɑːtɪdli/
KK: /daʊnˈhɑːrtɪdli/
In a way that shows sadness or disappointment.
She spoke downheartedly after hearing the bad news.
Downheartedly → It is formed from "downhearted" (where "down" means in a lower position and "hearted" comes from "heart" meaning emotional state) and "-ly" (meaning in a manner of). The word "downheartedly" means in a manner that reflects a low or sad emotional state.
Think of someone feeling 'down' in their emotions and acting in a 'manner' ('-ly') that shows sadness.