One day she was in the church of the Preaching Friars, which the Sisters of Penance of St. Dominic in Siena used to attend. The others had gone out, but she went on praying. Finally she came out of her ecstasy and got up to go home. All at once a light from heaven encircled her, and in the light appeared the Lord, holding in His holy hands a human heart, bright red and shining. At the appearance of the Author of Light she had fallen to the ground, trembling all over, but He came up to her, opened her left side once again and put the heart He was holding in His hands inside her, saying, “Dearest daughter, as I took your heart away from you the other day, now, you see, I am giving you mine, so that you can go on living with it for ever.” With these words He closed the opening He had made in her side, and as a sign of the miracle a scar remained on that part of her flesh, as I and others were told by her companions who saw it. When I determined to get to the truth, she herself was obliged to confess to me that this was so, and she added that never afterwards had she been able to say, “Lord, I give you my heart.”

After the reception of this heart, then, in such a gracious and marvellous way, from the abundance of its graces poured forth Catherine’s great works and her most marvellous revelations. In point of fact she never approached the sacred altar without being shown many things beyond the range of the senses, especially when she received Holy Communion. She often saw a baby hidden in the hands of the priest; sometimes it was a slightly older boy; or again, she might see a burning fiery furnace, into which the priest seemed to enter at the moment when he consumed the sacred Species. When she herself received the most adorable Sacrament, she would often smell such a strong sweet smell that she almost fainted. Seeing or receiving the Sacrament of the Altar always generated fresh and indescribable bliss in her soul, so that her heart would very often throb with joy within her breast, making such a loud noise that it could be heard even by her com­panions. At last, having noticed this so often, they told her con­fessor Fra Tommaso about it. He made a close inquiry into the matter and on finding it was true left the fact in writing as an imperishable record.

This noise bore no resemblance to the gurgling that goes on naturally in the human stomach; there was nothing natural about the noise at all. There is nothing surprising in the fact that a heart given in a supernatural way should act in a supernatural way too, for, as the Prophet says, “My heart and my flesh have rejoiced in the Living God,” that is to say, “They have jumped out, into the Living God.”

The Prophet says, “the living God”, to signify that this special beating or heart action, being caused by the true Life, does not bring death to the person to whom it happens as it would in the ordinary course of nature, but Life.

After the miraculous exchange of hearts the virgin felt a different person, and she said to her confessor Fra Tommaso, “Can’t you see, Father, that I am not the person I was, but am changed into someone else?” And she went on, “If only you could understand how I feel, Father! I don’t believe that anyone who really knew how I feel inside could be obstinate enough not to be softened or be proud enough not to humble himself – for all that I reveal is nothing compared to what I feel.” She described what she was experiencing, saying, “My mind is so full of joy and happiness that I am amazed my soul stays in my body.” And she also said, “There is so much heat in my soul that this material fire seems cool by comparison, rather than to be giving out heat; it seems to have gone out, rather than to be still burning.” And again, “This heat has generated in my mind a renewal of purity and humility, so that I seem to have gone back to the age of four or five. And at the same time so much love of my fellow-men has blazed up in me that I could face death for them cheerfully and with great joy in my heart.” All this she told her confessor alone, in secret; but from others she hid as much as she could.