This paper addresses the subject of the ‘prayer of the heart’ in Orthodox Christian asceticism, as displayed in the Philokalia, the eighteenth-century collection of patristic texts on the practice of contemplative prayer and deification, compiled by Sts. Macarius of Corinth and Nicodemus of the Holy Mountain. The ‘prayer of the heart’ is a composite practice, comprised of physical techniques combined with meditative methods, aiming to produce an emptying of the mind and the advent of the experience of deification through what is traditionally called ‘purification and guarding of the heart’. This paper contributes an analysis of the mystical anthropology employed by the Church Fathers focused on the human heart. The connection and interdependence between the physical and contemplative techniques is analysed and justified in a novel approach, before concluding with the way that the ‘prayer of the heart’ functions in one’s path towards deification.