“Whoever, including even the insects, has heard the name and mantra of Hayagriva only one time will never again fall into the lower paths.” 
Many great teachers in modern times have been requesting their students accumulate Hayagriva Heruka’s mantra, known to be particularly efficacious in these troubled times:
“a swift and powerful means to overcome negative forces and obstacles. Prayers to Hayagriva are especially beneficial in these degenerate times when sufferings and illnesses are rampant due to the strong delusions of sentient beings.” 
So important is Padma Heruka — the Lotus Hayagriva — that he was one of the main Enlightened deities the great Lotus-Born Padmasambhava practiced: “Glorious Hayagriva and Vajravarahi banished hindrances.”
Guru Rinpoche “arose in the form of Padma Heruka, ferocious and strong, the heruka of the secret sign” — Lady Yeshe Tsogyal 
Many illustrious Enlightened Masters taught and practiced Hayagriva as a Yidam aside from Padmasambhava, including the great Tibetan Yogi Shabkar, who was initiated by Chogyal Rinpoche. In his autobiography, Shabkar wrote:
“At dawn the following morning, he bestowed on us the maturing empowerment of the Victorious One, the Wish-fulfilling Gem, Hayagriva and Varahi. This is a profound and extraordinary teaching from the cycle of the new treasures. In heaven, the lineage of vidyadharas remains unbroken; on earth, the lines and colors of the mandala have not yet vanished; in between, the heaps of sacred substances have not yet diminished. Unsullied by demons and samaya-breakers, it still carries the fresh breath of both the wisdom dakinis and worldly dakinis.”
Hayagriva in modern times
Shabkar indicated in this quote that Hayagriva’s “mandala have not yet vanished.” In other words, Hayagriva is very much accessible to practitioners today — not just the ancient masters.
In modern terms, Hayagriva is the “Incredible Hulk” emanation of Amitabha and Chenrezig and Vajravarahi — his wisdom consort — is the ultimate Dakini. Despite his wrathful form, he is still chief among the compassionate, important in modern times.
Hayagriva — Chief among the Wrathful
As the Heruka of Amitabha’s Lotus Family, he is Chief among the Wrathful emanations, representing Dharma and Speech in its ferocious form — signified by the screaming (neighing) horse head bursting out of his fiery red hair.
“The Powerful Heruka is Hayagriva. Every being that lives in this world has no choice but to follow Hayagriva’s command. He is more powerful than any other being; there is no one to equal or even compete with him. Hayagriva is the universal ruler of all that appears and exists. His wisdom intent is enriched by the ‘three neighs’ – which is too vast a subject to explain right now. What you need to understand about Hayagriva … is that there is no one greater or more powerful than “the Powerful Heruka.” — Orgyen Tobgyal Rinpoche 
Hayagriva, the Wrathful Heruka, is the “Incredible Hulk” emanation of Amitabha and Chenrezig. As the Heruka of Amitabha’s Lotus Family, he is Chief among the Wrathful emanations, representing Dharma and Speech in its ferocious form — signified by the screaming (neighing) horse head bursting out of his fiery red hair.
Venerable Steve Carlier explains: “Hayagriva is a wrathful aspect of Chenresig. Making prayers to Hayagriva is a swift and powerful means to overcome negative forces and obstacles including those caused by spirit harms. Prayers to the deity are especially beneficial in these degenerate times when sufferings and illnesses are rampant due to the strong delusions of sentient beings. As a manifestation of Chenresig, the practice of Hayagriva also helps to develop compassion.” 
The brave practitioner who meditates on this this monstrously beautiful emanation can overcome obstacles quickly, and understand His cry of Wisdom (Dharma.) Hayagriva is also famous for very effective healing practices. [For a praise to Hayagriva see below. Hayagriva practice, though, normally requires teacher guidance and empowerment. Honoring and praising Hayagriva is fine for all people.]
Benefits of Practice of Yoga of Hayagriva
The benefits to the devotee who practices the Yoga of Hayagriva (NOTE: requires full initiation and permission of a lineage teacher) were stated in The Manifestation of the Superb Victorious Wrathful Great Horse Tantra:
“To the superb Initiation of the Fierce Hayagriva
And the victorious Tantra of great value!
If one surely beholds the initiation and has a fancy for it, he will be emancipated from fear and all diseases.
Those who practice the Yoga of Hayagriva, their patron Buddha,
Will be immune for seven hundred births from falling into the lower path and hell.
Those who have the faith and the pure realization constantly,
Will in their future life be born in the Pure Land.
If one recites each word of incantation 100,000 times,
Right in this life he shall see the face of Hayagriva.
Even in offering a part of the offerings to the Lord,
He will influence his surroundings and his neighbors.
Those who merely recite the incantation frequently
Will be free from the afflictions caused by evil spirits.”
The Tantra of Proud Master Hayagriva states:
“Those who practice the Yoga of Hayagriva will attain the Common and the Eight Superb Accomplishments. They will also obtain the Four Accomplishments of the Illumination-Holding (Yogi). He who does this will likewise attain the Three Bodies, the Four Bodies, the Five Bodies, and so on. He will also attain the Accomplishment of Mahamudra.”
The Secret Wrathful Hayagriva Tantra calls Hayagriva:
“the King of all Protections.”
Speech the Most Important Jewel
Of the three Jewels, it is often said by teachers that the most important is the Speech Jewel, the Dharma. The Buddha Jewel is our example, and the Sangha Jewel is our support, but it is the Dharma that points us to the path of Liberation and Enlightenment. Even if Buddha is gone beyond, and Sangha is not available to help us, the Dharma can always guide us.
This makes the Enlightened Deities of Speech the most important for day-to-day practice. For this reason, Amtibabha is the most most beloved Buddha after Shakyamuni Himself. Chenrezig (Avalokiteshvara) — an emanation of Amitabha — is the best-known of the Compassionate family of the Lotus. The compassionate Ones, the Lotus Family, represents Speech in Kriya, Yoga and Anuttarayoga Tantras.
Where “ordinary” pacifying speech and compassion are insufficient to the goal — the goal of Enlightenment, or removing the obstacles to Liberation — then normally a Vajrayana Buddhist turns to the Heruka or Wrathful emanations. A devotee of Amitabha, or Dharma, would seek out mighty Hayagriva.
Hayagriva — the Heruka of Speech
Symbolism is crucial in Vajrayana visualized meditations. Even so, many wonder why Hayagriva appears to have a green horse head bursting out of his wrathful fiery hair — the horse screaming with mouth wide open. A horses roar, the challenge of the stallion protecting his herd, is a terrible sound, piercing in intensity, carrying for miles in all directions.
The green represents “wind” and “action” — as with Green Tara. The ferocious horse scream is the penultimate symbolic roar of Dharma, carried on the winds to benefit all beings. Hayagriva is the ultimate “activity of the power of speech and Dharma.” Hayagriva is the Heruka emanation of Amitabha (and Chenrezig) and, as such, represents the most powerful aspect of speech or Dharma.
Why is Speech so Important?
Hayagriva’s Sanskrit “seed” syllable is Hrih, the same as Amitabha. At a sophisticated level of understanding, this single syllable Hrih is Hayagriva Himself. The seed syllable itself is also symbolic of the awesome power of sound, words, mantras, syllables, speech.
A single seed syllable, or a meaningful mantra, or a sutra or tantra text is often said to have the greatest impact in Buddhist practice. In this way, the three major emanations of Dharma Speech — Amitabha, Chenrezig and Hayagriva — are critical to Vajrayana practice. And, for those facing “obstacles” of any kind — afflictive emotions such as anger, illness such as cancer, poverty, or any issue that interferes with dedication to practice — Hayagriva is certainly the “go-to” Heruka.
All the key important aspects of Amitabha are “intensified” to its most wrathful level — Amitabha transformed into the Hulk-lilke version of Himself. All the symbols of Amitabha are still there: compassion, fire element, red, West, Lotus family (two-armed Hayagriva holds a red lotus), the aggregate of distinguishing (recognition), deep awareness of individualities, the Pure Land of Sukhavati (Western Paradise). And, importantly, as “Speech”, Hayagriva upholds the teachings of the sutra vehicles and the classes of tantra — perhaps in a more ferocious manner.
The great mantra
As the Heruka of the Speech and Lotus Family, Hayagriva’s mantra is particularly effective. Although practicing Hayagriva requires empowerment — a Highest Yoga Tantra practice — many people attend Empowerments to recieve blessings only. Geshe Tenley explains: “You may also attend as a blessing without taking vows or formal commitments. Geshe Tenley explains that when this empowerment is given in the monastery in India, many people come from afar to receive this powerful blessing.” 
Note: this chanting of the mantra is in the Tibetan style (see below):
Attending an empowerment for a blessing, or praying to Hayagriva, is beneficial to any sentient being. The main mantra is, as published on the Kurukulla Centre for Tibetan studies is:
“OM HRIH VAJRA KRODHA HAYAGRIVA HULU HULU HUM PHAT”
in Tibetan pronunciation this can sound like:
Om Hri Benza Todha Hayagiva Hulu Hulu Hum Pey
In 2018, Lama Zopa’s students accumulated vast numbers of the Hayagriva mantra, dedicated to the long life of their great teacher. In Lama Zopa’s letters to students, requesting healing, Hayagriva’s mantra is often recommended:
“Most Secret Hayagriva is the special protector deity of Sera Je Monastery, the monastery of Choden Rinpoche, Lama Zopa Rinpoche, Geshe Tsulga, Geshe Tenley and other teachers with connection to Kurukulla Center. Recently it has been advised to do as many Hayagriva mantras as possible dedicated to the long life of Lama Zopa Rinpoche, the Spiritual Director of Kurukulla Center.” 
On the Lama Yeshe Wisdom Archive, Lama Zopa recommended to a student who engages in healing for others:
“When you practice healing on someone in pain, one method is to visualize the moon syllable OM on your hand. It is white in color and its nature is light.
You should then recite the Most Secret Hayagriva mantra, which you need to memorize:
HRIH VAJRA KRODHA HAYAGRIVA HULU HULU HUM PHAT
While pressing your hand on the painful area, keep reciting this mantra.”
Hayagriva and great King Gesar
One of the most important and endearing stories in Tibet, Nepal and Mongolia is that of great King Gesar of Ling. Hayagriva — and horses — of course, plays a key role in this central story:
In the story of the birth of Gesar, published in the Shambhala Times, it was Hayagriva who empowered the hero’s magical horse, Kyang Go Karkar. 
At twelve-years of age, Gesar became King only after his magical horse, Kyang Go Karkar, won a competition horse race for the throne. It was an unfair match, since Kyang Go Karkar could actually fly — although in the race he kept his feet on the earth. [For a full story on King Gesar, see>>]
What is a Heruka?
Herukas — variously described as “Vira Heros”, “Wrathful Ones”, or even “Blood Drinkers” (due to complex symbolism associated with Charnel Grounds) — are the highest and fiercest emanations of Enlightened Deities. A Heruka should not be confused with “Heruka” as one of the names of Chakrasamvara (especially in Geulg School, He is often just called Heruka). A Heruka is normally a wrathful emanation of an important Buddha.
As wrathful emanations, they tend to take on the “activity” of the emanating Buddha. For example, Yamantaka, is the Heruka of Manjushri, who represents both “wisdom” and “body.” Hayagriva is the Heruka of Amitabha, who represents both “compassion” and “speech.” In other words, “Hulked-up Amitabha.” Vajrakilaya is Heruka emanation of Vajrasattva, and so on.
Hayagriva’s Terrifyingly Beautiful Appearance
As a Highest Yoga Tantra deity, Hayagriva appears often in YabYum, or in union with a consort representing wisdom. As an all-important Heruka of Dharma Speech, his consort is equally important, the Queen of the Dakinis Herself, Vajrayogini (usually appearing as Vajravarahi with the sow’s head). Vajrayogini appears blue in this union.
Hayagriva, as Amitabha, is a beautiful ruby red, representing not only fire, but the Padma family. Although he is “hulked up” and massive, with bristling muscles and gigantic form, and regardless of fangs and fiery hair, he is very beautiful in the ferociously masculine sense. Vajrayogini (varahi) is, as always, sensuous and stunningly beautiful, but with a slightly wrathful face. If he is the metaphorical Incredible Hulk, then she might be the irresistible vampire queen (in appearance).
There are different forms, notably, two-armed and six armed, and one-horse head versus three-horse heads. Both Nyingma and Gelugpa have three-horse head versions (in thee Gelugpa lineage, the six-armed Hayagriva has three horse heads). The two-armed emanation typically displays one face, and therefore also one horse head. The two-armed Hayagriva is usually in union with Vajrayogini (Varahi).
The symbolism of the two animals in important. Haygriva has a green horse, signifying fierce action speech. Vajravarahi (Vajrayogini) has a sows head, signifying wisdom (the sow’s head symbolically represents “triumph over ignorance.”) In other words, the ferocious compassion of Hayagriva (Horse: ferocious Dharma speech to liberate us) in union with the wisdom of Vajravarahi (Sow: triumph over ignorance.)
In the two-armed Gelugpa meditational deities, Hayagriva YabYum Vajrayogini (Vajra Varahi), ruby red Hayagriva holds a fiery red Lotus in his right hand, and nectar in a skullcup in his left. The fiery lotus is a most important symbol of the Padma (Lotus) Buddha Family of Amitabha. Lapis lazuli blue Vajrayogini carries her normal implements, flaying knife and skullcup. The symbolism of these wrathful implements has been covered previously. (For a story on wrathful deities, see this popular Buddha Weely Story>>)
Hayagriva ceremony for the long-life of the Dalai Lama at Sera Jey Monastic University:
Why the Horse?
The scream of the horse is piercing, ferocious, terrifying. A stallion’s roar can terrify a pack of wolves. Horses are also symbolic of WIND — in this context Lung (Tibetan), Prana (Sanskrit) and Chi (Chinese).
It is also said that Shakyamuni was born in the Asian year of the Horse.
Horses also represent swift fulfilment of wishes, both because of their association with Windhorse (usually visualized with the wish-fulfilling jewel on his back) and because in ancient times the horse was the symbol of wealth. A household would guard their horses above all other assets. Horses meant survival, prosperity, safety, happiness. The loss of a horse was treated as seriously as the loss of any other family member. The horse, in Tibet and Nepal, are the most sacred of sentient beings.
A Praise of Hayagriva
This is adapted from an old translated praise, but does not include any secret practices that require empowerment.
NOTE: Namo, namas translation — نمس नमस् namas, s.m. (often used as an interjection; and changeable in comp. to नमः nama, and नमो namo), Bowing, bending, making a bow;—a bow, salutation, reverential salutation, paying honour (by gesture or words); adoration, obeisance (performed by joining the palms and inclining the head;—often used in connection with the name of a deity.
Namo Haygriva, Wrathful Activity of the Padma Family!
Namo Hayagriva, Voice of Hrih, most Powerful of Sounds!
Namo Hayagriva, Most Wrathful and Beautiful Deity, Who Cuts All Root Poisons of Ignorance, Desire and Hatred!
Namo Lord Hayagriva, precious horse deity!
Namo Horse-Headed Hayagriva and Consort Vajra Varahi!
Namo Hayagriva! You are the wisdom body, speech and mind of all the buddhas of the ten directions,
The kingly Hayagriva, the Lord of Secrets,
Foremost among the wrathful.
The very thought of you crushes obstructing forces
To you I offer homage and praise!
Namo Hayagriva—fiercest manifestation of Avaolokiteshvara!
Namo Hayagriva—whose Voice is the cry of wisdom, the very syllable HRIH!
Namo Hayagriva—the very embodiment of the speech of all Buddhas!
Namo Hayagriva—who protects the wealth of the household and all horses!
Namo Hayagriva—Whose HRIH neigh frightens away all demons!
Namo Hayagriva—By Whose power Guru Rinpoche subdued powerful spirits and worldly deities!
Namo Hayagriva—whose horse voice cuts through all illusion!
Namo Hayagriva—who cures all illnesses!
Namo Hayagriva—lord of the horses sacred to Shakyamuni Buddha, Conqueror born in the year of the horse!
Namo Hayagriva—who subdues all nagas, snakes and sea spirits!
Namo Hayagriva—protector of the Dharma and of all wisdom!
Namo Hayagriva! Fiercest Avaolokiteshvara, cry out for us now, we implore you! Let your HRIH terrify and chase away all demons and evil! Let your HRIH protect our wealth and bring us prosperity, Lord Hayagriva! We pray to you to cure our illnesses by the very sound of your mighty HRIH! We ask you to cut through illusion and help us—and all beings—towards enlightenment.
The Eight Herukas
In the Nyingma Mahayoga tradition, there are the eight Enlightened Herukas, who are wrathful emanations of the major Enlightened deities.
First, the three of Body, Speech and Mind:
Then, the remaining five are:
 Venerable Steve Carlier “Secret Hayagriva Empowerment by Dagri Rinpoche” introduction>>
 Esoteric Teachings of the Tibetan Tantra, by C.A. Musés, 
 Lady of the Lotus Born: The Life and Enlightenment of Yeshe Tsogyal, Changchub, Gyalwa. Lady of the Lotus-Born: The Life and Enlightenment of Yeshe Tsogyal (Kindle Location 1243). Shambhala. Kindle Edition.
 Shabkar Tsogdruk Rangdrol. The Life of Shabkar: Autobiography of a Tibetan Yogin (Kindle Locations 2604-2609). Shambhala. Kindle Edition.