The origin of the Sacred Heart Devotion is very ancient, roots of it can be found as early as the second century. St. Bernard and St. Anselm in the 12th century promoted it, as well as Sts. Gertrude and Mechtild.
The Divine Mercy became well known from the diary of St. Faustina, a Polish nun in the 20th century.
Both of these devotions are covered in the links below.
Maresca has written: 'Heart to heart with Jesus' -- subject(s): Devotion to Sacred Heart, Sacred Heart, Devotion to
L. C. Berry has written: 'The favorite and favors of the sacred heart of Jesus' -- subject(s): Devotion to Sacred Heart, Sacred Heart, Devotion to
B. Hardy Welzel has written: 'The Sacred Heart and the Eucharist' -- subject(s): Devotion to Sacred Heart, Lord's Supper, Meditations, Sacred Heart, Devotion to
Annice Callahan has written: 'Spiritualities of the Heart' 'Karl Rahner's spirituality of the pierced Heart' -- subject(s): Devotion to Sacred Heart, History of doctrines, Sacred Heart, Devotion to
Peter J. Arnoudt has written: 'Of the imitation of the sacred heart of Jesus' -- subject(s): Devotion to Sacred Heart 'De imitatione sacri cordis Jesu' -- subject(s): Devotion to Sacred Heart
John A. Abruzzese has written: 'The theology of hearts in the writings of St. Francis de Sales' -- subject(s): Devotion to Sacred Heart, Sacred Heart, Devotion to
Alfred Yenveux has written: 'Religious and the Sacred Heart' -- subject(s): Catholic Church, Devotion to Sacred Heart, History and criticism, Prayers and devotions, Sacred Heart, Devotion to
Marguerite Marie Alacoque
Francis Larkin has written: 'Understanding the Heart' -- subject(s): Devotion to Immaculate Heart of Mary, Devotion to Sacred Heart, Miscellanea
Those devoted to the Sacred Heart of Jesus often pray to Saint Margaret Mary Alacoque, who had visions of Jesus revealing his Sacred Heart to her in the 17th century. She played a key role in promoting devotion to the Sacred Heart within the Catholic Church.
A symbol commonly associated with St. Margaret Mary Alacoque is the Sacred Heart of Jesus, as she was instrumental in promoting devotion to the Sacred Heart. Another symbol could be a lily, representing her purity and devotion to Christ.
This probably refers to the Sacred Heart of Christ, a symbol of divine compassion. It is used sarcastically by selfish people to describe compassionate people.