The Heart Sutra is preached on Vulture Peak, east of the ancient Indian city of Rajagraha, the capital of the kingdom of Magadha. Rajagraha, along with Sravasti, was one of the two major cities of ancient India most frequently visited by the Buddha during his forty-five year teaching career. The Vulture Peak is said to have been a favorite site of the Buddha, and here he gave a number of sermons to assemblies of monks and laypeople.
The rather unique prologue (of the longer version) introduces us to the leading characters of the sutra: Shakyamuni Buddha, Avalokitesvara Bodhisattva and Sariputra. The Buddha does not speak in the prologue, but enters into samadhi and silently empowers Sariputra to ask and Avalokitesvara to answer. The silence of the Buddha here is characteristic of much of Mahayana literature, and supports its classical view that the Buddha is "no longer simply the teacher but is transformed into the principle of enlightenment, a silent, eternal, numinous presence, the dharmakaya."
The Heart Sutra is the only Prajnaparamita text in which the Bodhisattva Avalokitesvara appears. His (or her) presence here is significant on several counts: first, it attests to the relatively late date of the sutra, a time when the cult of the Bodhisattva of Compassion, textually associated with the twenty-fourth chapter of the Lotus Sutra and the sutras of the Pure Land School, had become well-established. Secondly, the Heart Sutra is dedicated completely to the teaching of sunyata without any reference whatever to the other major theme of the Prajnaparamita sutras: compassion (which traditionally includes upaya or the Skillful Means of the bodhisattva.) The absence of this theme is countered, implicity, by the fact that the wisdom essential for the attainment of Buddhahood is proclaimed by a bodhisattva who is said to be the embodiment of compassion.
The presence of Sariputra is equally significant. The Heart Sutra does not inveigh against the Hinayana disciples of the Buddha, as is characteristic of the longer Mahayana sutras, in which the Hinayana disciples are considered inferior to the Bodhisattvas, both in their wisdom and in their aspiration to enlightenment. The presence of Sariputra here fulfills that function; Sariputra, in the Hinayana scriptures, is considered the wisest of the disciples of the Buddha, but here he comes across as perplexed and uninformed when asking Avalokitesvara how to practice the perfection of wisdom.