In the Brihat Tantra Sara, a large compilation of tantrik rites, Krishna appears as a fully-flowered tantrika devata, with his own yantra, gayatri, mantra and puja
or ritual which uses this yantra (click on this image for full size yantra). In the hexagon in the centre of the yantra, the following words appear: Krishnaya Govindaya Klim sadhya Gopijanavallabhaya Svaha. In the corners of the hexagon are the bija mantras Hrim and Shrim. Outside the hexagon is the Krisna mantra which runs: Klim Krishnaya Namah. In the petals of the yantra is a longer mantra Namah Kamadevaya Sarvajanapriyaya Sarvajansammohanaya Jvala Prajvala Sarvajanasya Hridayamavamsham Kurukura Svaha. Around the eight petals are the Matrikas or letters of the Sanskrit alphabet while in the angles of the protecting wall are bija mantras Hrim and Shrim, once more.
