Pope Pius XII instituted the feast of the Immaculate Heart of Mary in 1944 to be celebrated on August 22, thus replacing the traditional octave day of the Assumption (compare August 22 in the Tridentine Calendar with the same date on the General Roman Calendar as in 1954). In 1969 Pope Paul VI moved the celebration of the Immaculate Heart of Mary to the day (Saturday) immediately after the Solemnity of the Sacred Heart of Jesus. This means in practice that it is now held on the day before the third Sunday after Pentecost.
However, ...those who use the 1962 edition of the Roman Missal as an extraordinary form of the Roman Rite continue to follow the practice instituted by Pius XII in 1944.
The Catholic Encyclopedia
Mary began her journey along the road to perfection at a height to which other Saints arrived only at the end of a long life of saintliness. In all other children of Adam original sin prevented the divine generosity from having a free course. But mary was created immaculate, and therefore the grace of God streamed into her soul without check or hindrance. Her sinlessness, her heavenly purity, directed every action, every movement to God. Her heart was the pattern and model of all virtues, of all purity! "Blessed are the pure in heart!"
The Roman Missal, 1962
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