In the Bible, the word heart is often a figure of speech for the mind, will, and emotions. God's work of grace is performed in every believer's heart by the Holy Spirit. Through the gospel of Christ, God changes our hearts. That is to say, God changes our mind, will, and emotions.
God changes our mind. He transforms our mind by the Holy Spirit (Romans 12:1-2). Then we understand the power of the gospel (Romans 1:16). We repent and receive Jesus as our Lord (1 Corinthians 12:3). Repentance means a change of mind. That change is enabled by the Holy Spirit changing our hearts (Romans 2:28-29).
God changes our will. Once we had no desire for Christ. We were unwilling to receive Christ. Now, God has worked in our hearts with a desire for Christ (Philippians 2:13). That's the work of God in our hearts through the Holy Spirit (Philippians 1:6).
God changes our emotions. Once we had no tender emotions toward Christ nor remorse for our sins. Now, we have godly sorrow for our sins, and emotions of love and gratitude toward Jesus Christ (1 Corinthians 16:22; 2 Corinthians 7:9-10).
