The Heart Sutra is by far the most popular and well known Sutra in Japanese Buddhism regardless of the sects. Its Sanskrit title, Prajñāpāramitāhṛdaya, can be translated as "The Heart of the Perfection of Wisdom", and consists of 260 Chinese letters and contains the essence of Buddhist teachings.
There are Shinto priests who site this sutra during the rituals at their shrines, too.
It is no wonder, because Shinto and Buddhism had been equally respected and believed by the Japanese for a long time (Despite a short-time movements to abolish Buddhism based on the decree to separate Shintoism and Buddhism by the Meiji Government (1868) ).
In Buddhism, it is believed that by reciting or copying this sutra, one can attain peace of mind, free from suffering, or even get healed from illnesses. It is like a candle light shedding light of truth in the darkness of worldly sufferings.
The translation of the Heart Sutra from Sanskrit into Chinese is one of the great works by the famous Chinese priest, Xuanzang (Genjo Sanzo 玄奘三蔵), who lived in the 7th century during the Tang Dynasty in China.
He made a dangerous journey to India (across a desert and the mountains) in order to study Buddhism at the age of 33, and spent over ten years in India traveling and studying under various Buddhist masters. He studied one of the Buddhist teachings of “Consciousness-only” (Yuishiki-ron 唯識論) for five years at Nalanda Monastery in Northern India. He brought back as many as 657 books of sutras to China and devoted the rest of his life to translating them from Sanskrit to Chinese.
Thanks to his great works, Japanese scholar monks who were sent from Japanese government to China during Nara period (8th century) could bring back many books of sutras including the Heart Sutra to Japan.
In Japan to this day, the Heart Sutra are written and recited in Chinese. (well, not the same pronunciations, though..)
Yuishiki-ron is the doctrine that all phenomena are produced from seeds stored in alayashiki (the storage of consciousnesss).