The line you're referencing is:
> "Deep into that darkness peering, long I stood there wondering, fearing,
> Doubting, dreaming dreams no mortal ever dared to dream before;
> But the silence was unbroken, and the darkness gave no token,
> And the only word there spoken was the whispered word, 'Lenore?'
> This I whispered, and an echo murmured back the word, 'Lenore!'
> Merely this and nothing more.
>
> **Back into the chamber turning, all my soul within me burning,
> Soon again I heard a tapping somewhat louder than before.
> 'Surely,' said I, 'surely that is something at my window lattice;
> Let me see, then, what thereat is, and this mystery explore—
> Let my heart be still a moment and this mystery explore;—
> 'Tis the wind and nothing more.'**
>
> **Open here I flung the shutter, when, with many a flirt and flutter,
> In there stepped a stately raven of the saintly days of yore;
> Not a creature could be seen, and the night was stark and drear.
> Deep into the darkness peering, long I stood there wondering, fearing,
> Doubting, dreaming dreams no mortal ever dared to dream before;
> But the silence was unbroken, and the darkness gave no token,
> And the only word there spoken was the whispered word, 'Lenore?'
> This I whispered, and an echo murmured back the word, 'Lenore!'
> Merely this and nothing more.**
While the line you mentioned isn't explicitly stated, the implication is that the speaker's heart has cracked in two upon seeing the raven and hearing the echo of his lost love's name. This is a symbolic representation of his grief and despair.