The invention provides certain fused pyrazine compounds of the Formula (I) or a pharmaceutically acceptable salts thereof, wherein X, Y, R1, R3, R4a, R5a, R5b, R6, and the subscript t are as described herein. The compounds or their pharmaceutically acceptable salts can modulate the body's production of cyclic guanosine monophosphate (“cGMP”), and are generally suitable for the therapy and prophylaxis of diseases or disorders which are associated with a disturbed cGMP balance. The invention also provides pharmaceutical compositions which comprise compounds of Formula (I) or pharmaceutically acceptable salts thereof. The invention also relates to methods for use of the compounds or their pharmaceutically acceptable salts in the therapy and prophylaxis of the abovementioned diseases and disorders and for preparing pharmaceuticals for this purpose.