This is the 9622nd most frequent Spanish word.
arde
"Arde" means "burns" (from the verb "arder").
Here, 'arde' is used as the third-person singular present indicative form of 'arder', indicating that the firewood is in the process of burning.
La leña en la chimenea arde rápidamente.
The firewood in the fireplace burns quickly.
'Arde' here is metaphorical, describing intense feelings of excitement as if they were burning in one's heart.
Mi corazón arde de emoción por el reencuentro.
My heart burns with excitement about the reunion.
In this sentence, 'arde' describes the flame of the candle actively burning.