Is there any book or internet resource which has Prajñāpāramitā Hṛdaya Sūtra in Sanskrit and word to word English translation? I am not exactly looking for commentaries(though I don't mind commentaries accompanying word to word translations). The ones I found so far are only in English.
The prajnaparamita canon is quite ancient going back to 1-2 BCE. It's not clear if the original set of sutras were composed in Sanskrit or Gandhari first and subsequently translated to Sanskrit. (Source: Wikipedia)
However the heart (Hṛdaya) sutra, said to be part of the Prajñāpāramitā Sūtra canon, and most famous certainly, is in the view of modern historians and scholars almost certainly not part of the original Indian compositions. It was likely composed in Chinese and later rendered in Sanskrit.
This is a text that has caused a lot of confusion among students because it attempts to lay down the highest of realized truths using the inadequate vehicle of conventional language. Despite several attempts at translating it to be less obscure, it is a text that needs to be meditated upon, and not merely understood through the intellect reading it - (i.e. the language it is read in doesn't really matter as long as the translation is correct).
Here are some side by side Sanskrit-English translations:
... and one can find more of them using Google, but it is impossible to find the authentic original Sanskrit you're looking for (because there is none?).
The simple answer is that Edward Conze published a little book with his Diamond Sutra and Heart Sutra translations, and included the Sanskrit text of the Heart Sutra
Conze, Edward. (1975). Buddhist Wisdom Books : Containing the Diamond Sūtra and the Heart Sūtra. 2nd Ed. London : George Allen & Unwin. First Ed. 1957.
The book seems to be in print still and is moderately priced.
One little note however is that the Sanskrit contains a mistake. I discovered this in 2012 and finally published my explanation of the mistake and suggested correction earlier this year. It's quite minor, but important in how the text is interpreted.
Attwood, Jayarava (2015) Heart Murmurs: Some Problems with Conze’s Prajñāpāramitāhṛdaya. Journal of the Oxford Centre for Buddhist Studies. Vol 8, 2015. Paid Access until 2016.
I've produced a less technical and free summary of this article primarily for the Triratna community, but suitable for everyone.
I've also written a number of informal essays about the Sanskrit text, some of which are based on my study of the surviving manuscripts and some on the early Prajñāpāramitā tradition or the Chinese versions. A list of these essays can be found here.
This (in Romanised Sanskrit & English) should be of great help :
Prajna Paramita Heart Sutra in Sanskrit (prepared by: Dr. Michael E. Moriarty)
Check this video out. It has the Sanskrit version of the Sutra chanted in some 'Indian accent' and is easier to follow if you understand Sanskrit. The description has the sutra written in the Devanāgarī script and the caption has English and Tibetan translations.