Jesus informed St. Margaret Mary in 1675 that He desired the Sacred Heart Feast to be observed on the Friday following the Corpus Christi octave. In 1856, the Feast of the Sacred Heart was declared a universal feast. We observe June 7 as the Solemnity of the Sacred Heart of Jesus in 2024.

The human heart is a symbol of love. God's unending love for everyone was made visible to us via the Sacred Heart of Our Lord, whom we honor in this Catholic devotion. According to St. John Paul II, a fervent admirer of the Sacred Heart, "This feast reminds us of the mystery of God's love for the people of all times."

The early Christian era laid the groundwork for the Sacred Heart devotion. Sacred Scripture, especially the New Testament, has frequent references to God's love, and the Church Fathers also touch on this subject.

Christians would frequently meditate on Jesus' Five Wounds during the eleventh century, and it was from these meditations that the particular devotion to the Sacred Heart originated. Understanding of Jesus' Sacred Heart was advanced in the late 13th century by St. Gertrude the Great, who received personal revelations about it.

The first Sacred Heart Feast was observed by St. John Eudes in 1670, several centuries later. A French Visitation nun named St. Margaret Mary Alacoque experienced her own revelations from Jesus in 1673. In these, He revealed His love for everyone, even permitting St. Margaret to lay her head on His Heart—a gesture He had previously granted St. Gertrude. He requested Catholics worship Him in the Holy Eucharist and receive Holy Communion on the first Friday of each month.

In 1675, Jesus told St. Margaret that He desired an annual feast to honor His Sacred Heart. The Feast of the Sacred Heart was declared to be observed worldwide on the Friday after the Corpus Christi octave each year in 1856 by Blessed Pope Pius IX.

St. Margaret Mary Alacoque is revered as the patron saint of those devoted to the Sacred Heart of Jesus.

The Sacred Heart of Jesus made various promises to St. Margaret Mary Alacoque for those who practice this devotion faithfully:
1. I will give them all the graces necessary for their state of life.
2. I will give peace in their families.
3. I will console them in all their troubles.
4. I will be their refuge in life and especially in death.
5. I will abundantly bless all their undertakings.
6. Sinners shall find in my Heart the source and infinite ocean of mercy.
7. Tepid souls shall become fervent.
8. Fervent souls shall rise speedily to great perfection.
9. I will bless those places wherein the image of My Sacred Heart shall be exposed and venerated.
10. I will give to priests the power to touch the most hardened hearts.