Symbolism, Imagery, Allegory
We all know what hearts generally signify: valentines, romantic love, fidelity and passion. But Boccaccio uses the image of the heart in a far more complex and sinister way in some of the tragic stories told by the brigata. No construction-paper hearts on paper doilies for these folks.
In tales told by Fiammetta (IV.1, Ghismonda and Guiscardo) and Filostrato (IV.9, Rousillon and his wife), two male lovers have their hearts literally cut out by angry men as retribution for sexual indiscretion. Ghismonda's father, Tancredo, murders her lover Guiscardo and sends his heart to Ghismonda in a golden chalice. Rousillon extracts the heart of his wife's lover, has it diced, baked into a tasty casserole, and fed to his wife.
In Ghismonda's case, the heart's the symbol of Guiscardo himself. It represents his worthy qualities and the love he bears for her. It also comes to stand for Ghismonda herself, for when she sees the disembodied heart in the cup, it's as if her own life had been taken from her.
For both Ghismonda and Rousillon's wife, the act of consuming the lover's heart takes on special significance. Ghismonda "waters" the heart with her tears, mixes it with poison, and dies. Rousillon's wife literally licks the casserole plate clean, unknowing that she's just consumed her lover's heart. After the big reveal, she declares that she'll never eat anything more sublime than her lover's heart. There are erotic connotations linked with these acts of consuming, since the women are taking their lovers' bodies into their own bodies. But it's also an act of violence by the male authority figures in their lives.