The aim of this study is to analyse how the Hebrew word heart, לב, is used in the Old Testament: as an expression of the intellect, emotions, actions – all of those or only the intellect. The study also aims to see if the author, or groups of authors of the different texts where לב appears affect the use of the word. I work inductively with a lexical invention of the texts and I do an analysis on some different text to see if there are any differences.