Today is the feast of St. Margaret Mary Alacoque. She is the Saint of the Sacred Heart Devotion! Devotion to the Sacred Heart, as we know it, began about the year 1672. On repeated occasions, Jesus appeared to Saint Margaret Mary, a Visitation nun, in France, and He explained to her the devotion to His Sacred Heart as He wanted people to practice it. During the apparition He asked to be honored in the symbol of His Heart of flesh; he asked for acts of reparation, for frequent Communion, Communion on the First Friday of the month, and the keeping of the Holy Hour.
"And He [Christ] showed me that it was His great desire of being loved by men and of withdrawing them from the path of ruin that made Him form the design of manifesting His Heart to men, with all the treasures of love, of mercy, of grace, of sanctification and salvation which it contains, in order that those who desire to render Him and procure Him all the honour and love possible, might themselves be abundantly enriched with those divine treasures of which His heart is the source." — from Revelations of Our Lord to St. Mary Margaret Alacoque
To learn more about St. Margaret check out the New Advent page!