The decoration of the chapel’s dome refers to Casimir’s piety and virtue. Sculptures symbolising temperance, justice, fortitude and prudence stand in the niches between the windows.

The virtue of Justice is represented by a woman holding a pair of scales, a symbol of fairness and impartiality, in her right hand. In her left hand, she holds a sword to protect the righteous and punish the guilty. Next to her is an ostrich, a symbol of justice. It was believed that this bird can digest iron, and all its feathers are of equal length.

The virtue of Fortitude is symbolised by an armour-clad woman. In her right hand, she is holding an oak staff, showing strength of spirit; and with her left hand she is leaning on a column, signifying constancy. Next to her is a lion, a symbol of wisdom and power.

The figure depicting the virtue of Prudence is holding a mirror, a symbol of self-knowledge. In her right hand she is holding a fish, referring to well-judged, prudent actions. Next to her is an elk, which was considered a wise animal, for even when running swiftly it does not get caught up in shrubbery.

The figure representing the virtue of Temperance is diluting wine with water. An elephant standing nearby also embodies moderation. It was believed that this animal never eats more than necessary, and puts aside the rest for the next day.

There are four painted compositions in the dome’s pendentives: Chastity and Virtue above the entrance (by Franciszek Smuglewicz), and St Casimir’s Hymn to the Blessed Virgin Mary and St Casimir Accompanied to Heaven above the altar (by Michelangelo Palloni). At the apex of the dome is a dove, a symbol of the Holy Spirit.