This great feast in the Church is always celebrated on the octave day of Corpus Christi, the feast which celebrates the Body and Blood of Christ.
Corpus Christi falls on the Thursday after Trinity Sunday (which itself falls on the Sunday after Pentecost), which means the feast of the Sacred Heart falls nineteen days after Pentecost Sunday.
The following day is the feast of the Immaculate Heart of Mary, so these two devotions to the hearts of Jesus and Mary are side-by-side on the liturgical calendar.
Prayer to the Immaculate Heart
of Mary
Immaculate Heart of Mary,
prayer for us, now and at the hour of our death, Amen.
(say 3 times)