The word “heart” appears in the Bible 895 times in various contexts. It was used when people made major decisions or showed feelings toward someone or a situation. Today, many people use it to describe their feelings toward God. Jesus looked at the hearts of many people (whether they knew it or not) to discern their true intentions. Many people use the phrase “God knows my heart,” and indeed He does, but that can be a dangerous statement. He’s been dealing with hearts from the beginning and is the only expert on them. God knows everyone's heart, and it’s vital we give it all to him. 

Ref. Joel 2:13, Heb. 10:22, 1 Pet 3:15, 1 John 3:20.