Heshang Moheyan (Chinese: 和尚摩訶衍; pinyin: Héshang Móhēyǎn) was a late 8th century Buddhist monk associated with the East Mountain Teaching. Moheyan (摩訶衍) is a brief translation of Mahayana in Chinese, so the name literally means a Mahayana monk. He became famous for representing Chan Buddhism in the so called "Council of Lhasa," a debate between adherents of the Indian teachings of "gradual enlightenment" and the Chinese teachings of "sudden enlightenment," which according to tradition was won by the "gradual teachings."

Hwashang is a Tibetan approximation of the Chinese héshàng "Buddhist monk (Chinese: 和尚). This, in turn, comes from the Sanskrit title upādhyāya "teacher".

Whilst the East Mountain Teachings (known as "Northern School" Chan) were in decline in China, having been attacked by Shenhui (a student of Huineng) as a supposed "gradual enlightenment" teaching, Moheyan traveled to Dunhuang, which at the time belonged to the Tibetan Empire, in 781 or 787. For Moheyan, this was a new opportunity for the spread of (Northern) Chan. However, as van Schaik observes, the exclusive association of Moheyan with the Northern School is problematic, as Moheyan may have actually counted Shenhui as one of his teachers, and texts containing Moheyan's teachings exhibit an attempt at harmonizing sudden and gradual aspects of practice.

Luis Gómez observes that while Moheyan's sectarian affiliations are unclear, he seems to have belonged to a late Northern branch which leaned strongly toward Southern Chan teachings. Gómez regards Moheyan as doctrinally closer to the sudden teaching of the Southern School than Northern gradualism. For Gómez, Moheyan's doctrinal stance is more important than his lineage affiliation, which he regards a matter of religious politics. There is also evidence that Moheyan had connections to the Baotang school. However, according to Gómez, the exclusive focus on "spiritual lineage" in the traditional sense overlooks that Moheyan was not trying to conform to a received doctrine. Gómez states rather that "he [Moheyan] was his own man, a moderately creative religious specialist who borrowed and innovated at will. The concepts of 'teacher' and 'lineage' serve a variety of ahistorical functions in his hagiography, as they do in that of so many other Buddhist masters—they are devices for recognizing or claiming inspiration, influence, and political and institutional allegiance."

After teaching in the area of Dunhuang, Moheyan was invited by Trisong Detsen of the Tibetan Empire to settle at Samye, then the center of emerging Tibetan Buddhism. Moheyan promulgated a variety of Chan Buddhism and disseminated teachings from Samye where he attracted a considerable number of followers.

However, in 793 Trisong Detsen resolved that Moheyan did not hold the true Dharma. Following intense protests from Moheyan’s supporters, Trisong Detsen proposed to settle the matter by sponsoring a debate. The most famous of these debates has become known as the "Council of Lhasa", although it may have taken place at Samye, a considerable distance from Lhasa. For the famed Council of Lhasa, an Indian monk named Kamalaśīla was invited to represent Indian Buddhism, while Moheyan represented Chinese Chan Buddhism.

While Moheyan took a subitist approach to enlightenment. In this view, practices such as the perfection of morality, and studying Buddhist texts was seen as "gradualist", and Moheyan held that these were only necessary for those of "dim" facility and "dull" propensity. Those of "sharp" and "keen" facility and propensity do not need these practices, as they have "direct" access to the truth through meditation. This concession to the "gradualists", that not everyone can achieve the highest state of meditation, left Moheyan open to the charge that he had a dualistic approach to practice. To overcome these inconsistencies in his thesis, Moheyan claimed that when one gave up all conceptions, an automatic, all-at-once attainment of virtue resulted. He taught that there was an "internal" practice to gain insight and liberate one-self, and an "external" practice to liberate others (upaya, or skillful means). These were seen as two independent practices, a concession to human psychology and scriptural tradition.

According to José Cabezón: