The Heart Sutra, formally the Prajnaparamita Hridaya, the heart of the perfection of wisdom, compresses the vast Prajnaparamita literature into a text short enough to be chanted daily across East Asian Buddhism, and its most quoted line, form is emptiness and emptiness is form, states prajna's content as directly as the tradition ever states it: not that phenomena fail to exist at all, a position Mahayana philosophy explicitly rejects as nihilism, but that they exist without the independent, self sufficient nature ordinary perception projects onto them, arising instead interdependently, conditioned by everything around them.
Edward Conze's widely used translation and study of the sutra, paired with the Diamond Sutra in a single volume, situates the text within a corpus that developed over several centuries beginning in the early centuries CE, arguing wisdom by progressive negation, denying fixed existence to one category of phenomenon after another, the aggregates, the sense faculties, even the four noble truths themselves, until nothing is left standing as an exception to emptiness, including emptiness's own status as a fixed doctrine to cling to. This last move, emptiness emptied of itself, is what commentators point to when explaining why prajna cannot be reduced to a philosophical position memorised and affirmed; the perfection names a way of directly seeing that leaves the practitioner unable to grasp even the correct teaching as a fixed possession.