From Science and Health with Key to the Scriptures by Mary Baker Eddy:

Heart: Mortal feelings, motives, affections, joys, and sorrows. (587: 23)

Man walks in the direction towards which he looks, and where his treasure is, there will his heart be also. (451:14-16)

We should examine ourselves and learn what is the affection and purpose of the heart, for in this way only can we learn what we honestly are. (8:28)

Jesus prayed; he withdrew from the material senses to refresh his heart with brighter, with spiritual views. (32:25)

Through spiritual sense you can discern the heart of divinity, and thus begin to comprehend in Science the generic term man. (258:31)

Who that has felt the loss of human peace has not gained stronger desires for spiritual joy? The aspiration after heavenly good comes even before we discover what belongs to wisdom and Love. The loss of earthly hopes and pleasures brightens the ascending path of many a heart. (265:23-28)

Human affection is not poured forth vainly, even though it meet no return. Love enriches the nature, enlarging, purifying, and elevating it. The wintry blasts of earth may uproot the flowers of affection, and scatter them to the winds; but this severance of fleshly ties serves to unite thought more closely to God, for Love supports the struggling heart until it ceases to sigh over the world and begins to unfold its wings for heaven. (57:22)

The vital part, the heart and soul of Christian Science, is Love. (113:5-6)

Happy Valentine’s Day!