The Bible speaks of the heart in Proverbs, in the prophet Jeremiah, and in Jesus’ teaching on treasure.
In Proverbs 4:23:
23 Keep thy heart with all diligence; for out of it are the issues of life.
In Jeremiah 17:9:
9 The heart is deceitful above all things, and desperately wicked: who can know it?
In Matthew 6:21:
21 For where your treasure is, there will your heart be also.