When did feast of IHM get changed?

[drummerboy]

I was always under the impression that Aug. 22 was the feast of the Immaculate Heart of Mary; it seems it was made such by Pius XII, looking through my original, pre-VII Mary My Hope prayer book.  But now its on June 28, immediately after fest of the Sacred Heart on the 27th.  Now I remember that Christ asked for such a feast the Friday after Corpus Christi; did the Church place the feast of the IHM after the Sacred Heart to both preserve the feast of the Coronation of Mary, on Aug. 22, and also to keep the "two Hearts" feasts' more closely united?