Immaculati Cordis Beatæ Mariæ Virginis ~

 Duplex II. classis

Tempora: Feria Quinta infra Hebdomadam XIII post Octavam Pentecostes III. Romanism 

The liturgical worship, through which due honor is given to the Immaculate Heart of the Virgin Mary, and for which many holy men and women have prepared the way, the Apostolic See itself first approved in the beginning of the nineteenth century, when Pope Pius VII instituted the feast of the Most Pure Heart of the Virgin Mary, to be piously and reverently celebrated by all the dioceses and religious families who had asked for it. Afterwards Pope Pius IX added an Office and a proper Mass to it. But an ardent desire and longing, which had arisen in the seventeenth century, grew day by day, that namely, the same Feast, given greater solemnity, might be spread to the entire Church. In 1942, Pope Pius XII, graciously acceding to this wish, and during the terrible war then ravaging almost the entire world, pitying the infinite hardships of men, and because of his devotion and confidence in our heavenly Mother, in solemn supplication earnestly entrusted the entire human race to her most generous Heart, and in honor of the same Immaculate Heart he ordered a Feast to be kept forever with its proper Office and Mass.

- From ecclesiastical documents, Breviarium Romanum