Yes, HETEROCYCLES is a Scrabble word!

Letter values in Scrabble US: H 4, E 1, T 1, E 1, R 1, O 1, C 3, Y 4, C 3, L 1, E 1, S 1.

Is it a valid word?

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

a compound containing a heterocyclic ring
a ring of atoms of more than one kind; especially a ring of carbon atoms containing at least one atom that is not carbon

Also: heterocyclic compound, heterocyclic ring.