The tiny book “The Heart Sutra Explained” (230 pages) includes commentaries by Indian and Tibetan sages.
These commentaries are very useful to study the Heart Sutra from different perspectives.
E.g.: a commentary on the first line in the prologue “Thus I have hear at one time”:
“The commentator Vajrapani has high praise for the word Thus (“evam” in Sanskrit), the word with which sutras begin. Those four letters are the source of the 84.000 doctrines taught by Buddha and are the basis of all marvels. The meaning of the other words are less clear, there is controversy over the “I” who heard them and to the meaning of “at one time””.
The high praise of Thus – “evam” – is quite similar to the commentary of Bernie Glassman who says in “The Dude and the Zen Master” that the Heart Sutra begins with the most important word “Avalokiteshvara” or even better with the letter “A”. If this “A” is wholly encompassed, the Heart Sutra is all encompassed.
The controversy over the “I” who heard them and to the meaning of “at one time” may be seen as Buddhist question (or Koan) in my opinion .
This example given is only one of the many commentaries.
Next to this tiny book, a basic knowledge of Sanskrit is very helpful for a further study of the Heart Sutra.
“The Heart Sutra Explained” is highly recommended for a further study of the Heart Sutra from different perspectives, as is a basic course of Sanskrit.
For a first reading and basic study of the Heart Sutra, Red Pine’s translation and commentary is highly recommended.
For a first reading and more poetic commentary, “The Heart of Understanding” by Thich Nhat Hahn is also highly recommended.