Heart Essence (snying thig). In general identical with the Instruction Section (man ngag sde]]), the third of three division of Dzogchen. In particular it refers to the Innermost Unexcelled Cycle of Heart Essence (yang gsang bla na med pa'i snying thig gi skor), the fourth of the four divisions of the Instruction Section according to the arrangement of Shri Singha.
All lineages of the Innermost Essence passed through Shri Singha and continued in Tibet through his personal disciples, Padmasambhava and Vimalamitra. In the 14th century these two lineages passed through Rangjung Dorje, the third Karmapa, and his close Dharma friend Longchen Rabjam (1308-1363), the latter of which systematized these teachings in his great body of writings. The Nyingtig teachings have also appeared through many other lines of transmission; for instance, each major tertön reveals an independent cycle of Dzogchen instructions. The practice of the innermost Heart Essence is continued to this very day.