In the Orthodox tradition the emphasis of knowledge and emotion is centered in the heart.
For the Bible the innermost topos-place for the human knowledge, feelings and decisions is the "heart." (Isaiah 65:14; Jeremiah 24:7; Luke 2:19). For the Gospels the heart is the principle of good and evil thoughts. (Mark 7: 21; Luke 6:45). The heart is the seat of wisdom (1 Kings 3:12) and for Saint Paul the heart is the instrument of faith through the Holy Spirit. The Spirit dwells in the heart. (Rom.5:5) This theme has been maintained in the Church fathers and is still central in the Orthodox Christian tradition and practice. Kardiognosis (knowledge of the heart) is still an Orthodox practice that the spiritual director must have an insight into the human heart in its yearning for God. God sees the heart and does not judge people on outward appearances. Jesus Himself knew the secrets of the heart (Mark 2:6-8; John 2:25), that is, He had an insight into the "hidden person of the heart" (1 Peter 3:4). The spiritual father is expected to discern the innermost thoughts, the heart, of those he counsels. A popular Orthodox tradition is "the prayer of the heart." This prayer is "Lord Jesus Christ have mercy on me." (Mark 10:49; Luke 23:42) This became a monastic spirituality with its desire to "pray without ceasing" (1Thessaloinans 5:17) especially it became a strong practice in the tradition of Hesychasm.
Hesychasm is expressed in an ascetical life and aims to attain the vision of the uncreated light, that is theosis-glorification. This is through the remembrance of the divine name or the Jesus prayer or the guarding of the heart. Hesychasm can simply be described as the prayer of the heart mysticism.
The Western, Roman Catholic, scholasticism term "heart" even though it is a biblical concept finds it too unspecific and prefers the faculties of the soul (intellect, will and emotion). That is, a rationalistic approach to God expressed in the scholastic terms of "faith seeking understanding." Contrary to this the theological synthesis of Saint Gregory Palamas who was defender of hesychastic prayer of the heart rejected rationalism regarding the relation of the human person with God. To avoid pantheism he made a distinction between the essence and the uncreated energies of God. The essence is totally transcendent and unapproachable by creatures and the energies shared who practice the Jesus prayer. This Orthodox spirituality, mysticism of the heart, is found in the Philokalia. This is a personal contact and experience of God's love in our heart. It is the feeling of the presence of God in our innermost being.