Concentration is not thinking of one thing. On the contrary, it is excluding all thoughts, since all thoughts obstruct the sense of one's true being. All efforts are to be directed simply to removing the veil of ignorance. Concentrating the mind solely on the Self will lead to happiness or bliss. Drawing in the thoughts, restraining them and preventing them from straying outwards is called detachment (vairagya). Fixing them in the Self is spiritual practice (sadhana). Concentrating on the heart is the same as concentrating on the Self. Heart is another name for Self.