In the three worlds all Buddhas
The "three worlds" are the worlds of past, present and future (sometimes also referred to as the worlds of form, formlessness, and desire.) The vehicle through which the Buddhas attain their Buddhahood is the Transcendent Wisdom of sunyata.
Anuttara Samyak Sambhodi means "Perfect Unexcelled Awakening." It is the enlightenment of a perfect Buddha, one who has by himself rediscovered the teaching that leads to liberation. Anuttara Samyak Sambodhi also means possession of the "ten powers" (Sanskrit: Dashabala) of a perfect Buddha:
The "attainment" of these ten powers in Anuttara Samyak Sambodhi may seem, on the surface, a logical contradiction since the sutra has just declared that there is "no attainment, with nothing to attain." The implicit message here is that in and of itself Anuttara Samyak Sambodhi too is empty but the ten powers arising out of deep contemplation on the wisdom of sunyata can be used as "skillful means" (Sanskrit: upaya) which, along with wisdom and compassion, are the hallmark of a bodhisattva in the Mahayana literature. Having these ten powers at his or her disposal, the bodhisattva works tirelessly to save all beings, knowing fully well that all is inherently empty. The effort is directed toward helping individuals change their karmic legacies and patterns rather than "saving" any solidity called "being."
Anuttara Samyak Sambodhi changes the complexion of the sutra from a mere negation of Hinayana categories to a positive fullfillment of the bodhisattva vow ("Sentient beings are numberless; I vow to save them all.") The bodhisattva treads on this path immersed in the intuitive wisdom of sunyata rather than the rational categories of the Hinayana model or having the illusion that there is someone who can "save" someone. The wisdom of sunyata is not an opinion or a category but an experience; it is an experience in which "sunyata is" rather than "sunyata is something." The experiencer and the experienced are inseparable, indistinguishable from each other. The bodhisattva and those he or she is trying to "save" are inseparable from each other.
In the sense of celebrating the insight into sunyata, the sutra ends here. Historically, however, by the time the Heart Sutra was given its final shape, the influence of Mantrayana (the vehicle of mantra practice) and Tantra was clearly ascendent within Mahayana. The following passage is to be seen, therefore, in historical context as an addendum and proselytizing in nature. The assertions made here clearly contradict the insights presented earlier in the sutra. Commentators through the ages have taken opposite positions on the inclusion of the mantra in the sutra; perhaps the best way to sum up the place of the mantra in the sutra is to note the historical context and leave it entirely up to the reader--to use this mantra as an incantation, as a tool of power; a more discerning inquirer may see the mantra as a linguistic and symbolic summation of the central teaching of the Mahayana wisdom schools.
A very positive view of this mantra is offered by Thich Nhat Hanh, the contemporary Vietnamese Zen master: