http://catholicharboroffaithandmorals.com/Immaculate%20Heart%20of%20Mary.html

Devotion to the Heart of Mary is but the consequence of the devotion due to the Heart of Jesus. It is a consequence of that boundless love of Jesus for his most holy Mother, which leads him to share with her all the riches and honors, so far as they can be communicated to a creature. The Church never disassociates the Mother with her Divine Son in the festivals which she celebrates in his honor. If she celebrates the mysteries of the Savior, from his Incarnation to his Ascension, she celebrates likewise all the mysteries of Mary, from her Conceptions to her Assumption. The feast of the Sacred Heart of Mary (Immaculate Heart of Mary) is, therefore, but the natural consequence of the Feast of the Sacred Heart of Jesus.