Catechism of the Catholic Church §1432 — excerpt
The human heart is heavy and hardened. God must give man a new heart. Conversion is first of all a work of the grace of God who makes our hearts return to him: "Restore us to thyself, O LORD, that we may be restored!"
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.