You only have to see from where the 'I' springs.

Question: What is the Heart referred to in the verse of Upadesa Saram where it is said, ‘Abiding in the Heart is the best Karma, Yoga, Bhakti (devotion) and Jnana (knowledge)?

Sri Ramana Maharshi: That which is the source of all, that in which all live, and that into which all finally merge, is the Heart referred to.

Question: How can we conceive of such a Heart?

Sri Ramana Maharshi: Why should you conceive of anything? You have only to see from where the ‘I’ springs. That from which all thoughts of embodied beings issue forth is called the Heart. All descriptions of it are only mental concepts.

~ Be As You Are: The Teachings of Sri Ramana Maharshi, edited by David Godman