St. Catherine of Siena (d. 1380) was a Dominican tertiary who lived in Italy. A tertiary is a member of a Catholic religious order (like the Carmelites or the Franciscans, etc.) that live outside the monastery or the convent. Because they live in the world the rules of their order have been modified.
This young woman had the pious habit of praying that Almighty God would take her whole mind, heart and will unto Himself. And Our Lord, Who will always reward the sincerity and perseverance of a holy petition, answered Saint Catherine’s prayers in a very real way.
His miraculous reply came through a series of apparitions, at the end of which He had taken her heart for Himself. Then nearing Catherine, Jesus held out His own Sacred Heart.
"Dearest daughter," He said tenderly, "as I took your heart for Myself, now I am giving you Mine, so that you can go on living with It forever."
Then Our Lord healed the wound made in her side,