Yes, HEROISM is a Scrabble word!

Letter values in Scrabble US: H 4, E 1, R 1, O 1, I 1, S 1, M 3.

Is it a valid word?

HEROISM is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the qualities of a hero or heroine; exceptional or heroic courage when facing danger (especially in battle)

Not playable in Scrabble US: VALOROUSNESS.