"We say that noetic prayer is for all Christians. Noetic prayer is also called prayer of the heart. You ask if oral prayer can also be called prayer of the heart. If prayer is not pure, neither noetic not oral prayer can be called prayer of the heart. Prayer of the heart is the prayer where the mind is literally swallowed up by the heart. Bombs can be falling, the house burning; the mind has no intention of leaving the heart, even if it;s in danger of burning.
That's why we must also cultivate the virtues and unceasing prayer. As much as we can, never stop saying, 'Lord Jesus Christ have mercy on me' orally and from the heart. When you get used to saying constantly, "Lord Jesus Christ have mercy one me', then you are sweetened so much that you are drawn to say this little prayer constantly. You don't feel hungry, nor do you want to talk, or say anything else."
"Well, do you want me to tell you how we, uneducated new, read the Holy Bile? Having prayed for five to six hours, I then read the Holy Bible and by preference, the four Gospels. as to a brother, I assure you that my mind is so enlightened, I understand so clearly, that I can't cope with the overwhelming sentiments. I leave the book and weep with a lot of emotion for a long time." -- Preface
Author: Monk Joseph Dionysiatis