The mosaic over the choir, entitled The Triumph of the Sacred Heart of Jesus, is the largest and most important work of art in the church. It was created by Luc-Olivier Merson, H. M. Magne and R. Martin, and was dedicated in 1923. The mosaic is composed of 25,000 enamelled and gilded pieces of ceramic, and covers 475 square meters, making it one of the largest mosaics in the world.
The central figure is Jesus Christ, dressed in white, with open arms offering his heart, decorated with gold. He is joined by his mother, the Virgin Mary, and by the Archangel Michael, the protector of the church and of France. At his feet, kneeling, is Saint Joan of Arc offering him a crown. A figure of Pope Leo XIII offers a globe to Christ, symbolising the world.To the right of Christ is a scene titled "The Homage of France to the Sacred Heart;" a group of popes and cardinals present a model of the basilica to Christ. On his left is "The Homage of the Catholic Church to the Sacred Heart": where people in the costumes of the five continents pay their homage to the Sacred Heart.