The interior has a single nave with a barrel-vaulted roof subdivided into five spans by pilasters and arches, with four side-chapels. The first chapel to the right is the great chapel ("cappellone") of the Sacred Heart, very elongated and arranged like a miniature church in itself, mirroring the cathedral in which it is set: the end part contains four little side chapels and a larger chapel under an octagonal cupola.
The archway leading to the presbytery is narrower than the nave and flanked by two pilasters. The presbytery itself, which is very deep, is covered by an octagonal cupola (planned in the opening years of the 19th century by the architect Domenico Franco) and finished by a semi-circular apse, separated from the nave by a marble balustrade. Three steps lead to the presbytery; at the foot of the central stair are two marble lions. The high altar is also of marble of the 17th century, crowned by statues of Our Lady of the Immaculate Conception and of Saints Emilius and Priamus, patrons of the town. To either side of the altar are the inlaid wooden choir stalls. The frescos are by the Parma artist Emilio Scherer, between 1877 and 1878." (Text from Wikipedia).