This volume contains two Tantras: the Tantra of Great Bliss and the Tantra of the Natural Intent of the Heart. Both of these Tantras represent a meeting of the Atiyoga tradition and the Mahayoga, and offer us an insight into the interrelationship of these two classes of Tantra as they are brought together. We are gradually introduced to a seed syllable and to mandalas both physical and sonic, elaborately described in colorful detail. Practices are described, including a graphic description of sexual yoga, while we are reminded that there is no practice or meditation. The translations in this book were done based on Tibetan manuscripts, images of which are included. The Indian source works have been lost in time. The Tibetan texts we have are translations made by Vairochana, a famous Tibetan translator who went to India in search of the literature on instantaneous enlightenment in the Eighth Century of our era. His biography recounts his finding a teacher, Sri Singha, who had the transmission, but did not have the books, as the King had put them under lock and seal due to a disturbance involving a prostitute and a nun. So Sri Singha and Vairochana broke in to the palace by night, broke the seals, and stole the books. Then, over a period of many years, Vairochana studied these texts under Sri Singha. It is certain that Vairochana carried finished translations of several works with him when he returned to his country. The Tantras here translated are among the source works that inspired such great Tibetan luminaries as Longchen Rabjampa (1308-1364), Jigme Lingpa (1729-1798), and Mipham Gyatso (1846-1912). It is clear that the thinking within them was found critical to an understanding of the profundities of the Great Perfection, even hundreds of years after Vairochana's translation, and that those who sought to reconcile the inspiration of the Great Perfection with the practical realities of a practicing path, such as the Mahayoga, found them to be critical to their understanding. The Tantras come to us from out of the same basic time period as the works of Saraha, and do discuss the Mahamudra at numerous points. Those who study the early roots of the Mahamudra transmission and its relationship to the Great Perfection transmission will find these Tantras helpful. Those who study the debate regarding instant verses gradual enlightenment will find these works a valuable resource.