Snying thig skor bzhi

Menngagde itself is sometimes said to have been further divided by Sri Singha into four categories, called the "Four Cycles of Nyingtig" (Wylie: snying thig skor bzhi).

They are the:

1. Outer Cycle
2. Inner Cycle
3. Secret Cycle
4. Innermost Unexcelled Cycle (Wylie: yang gsang bla na med pa'i snying thig gi skor)

Variations of the name of the fourth section include the Secret Heart Essence (gsang ba snying thig), the Most Secret Unexcelled Nyingtig (yang gsang bla na med pa snying tig), the Innermost Unexcelled Cycle of Nyingtig (yang gsang bla na med pa'i snying thig skor), the Most Secret and Unexcelled Great Perfection (yang gsang bla na med pa rdzogs pa chen po), the Most Secret Heart Essence (yang gsang snying thig), the Most Secret Unsurpassable Cycle (yang gsang bla na med pa'i sde) and the Vajra Heart Essence.