50 Whatever the image employed, it is clear that the living heart of Christ – not its representation – is the object of our worship, for it is part of his holy risen body, which is inseparable from the Son of God who assumed that body forever. We worship it because it is “the heart of the Person of the Word, to whom it is inseparably united”. Nor do we worship it for its own sake, but because with this heart the incarnate Son is alive, loves us and receives our love in return. Any act of love or worship of his heart is thus “really and truly given to Christ himself”, since it spontaneously refers back to him and is “a symbol and a tender image of the infinite love of Jesus Christ”.
Source: Dilexit Nos (Vatican.va)