This paper attempts to analyze the instances and contexts of the use of the concept “heart”, which is the key concept for Christian anthropology, based on the material of Old Irish church literature, namely, on the treatise Apgitir chrábaid. The following cases of using the word “heart” in the studied text are revealed: “love for God in the heart”, “fear of God in the heart”, “purity of the heart”, “simplicity of the heart”, “confession of something in the heart”, “heart as a container of faith” , “heart as the dwelling place of God”, “heart as the place where the Truth is”. These cases are grouped by the author into types. It was done so in order to review them within the conceptual grid, built by various researchers, who utilized the idea of different semantic base for each case of the “heart” usage in Christian literature of Early Middle Ages. “Heart” usage groups were formed as 1) a physical organ 2) the emotion center 3) the intelligence center 4) the center of willpower and desires 5) the center of spiritual life and religious experience 6) the symbolic core of a human being, the synonym of a human being in general, spirit or soul in particular. An assumption is made about the presence of an intertextual connection between some fragments of the Apgitir chrábaid where the concept of “heart” is present and a number of biblical texts (Gospel of John, Epistle to the Ephesians, The Second Epistle of Peter).