The present invention provides imidazopyridazine compounds or imidazothiadiazole compounds of Formula I having the structure: (I) wherein X1, X2, X3, X4, X5, Y, W, R1, R2, R3, R4, R5 and (II) are as defined herein, or a stereoisomer, tautomer, pharmaceutically acceptable salt, prodrug ester or solvate form thereof. These compounds are inhibitors of platelet aggregation and thus can be used as medicaments for treating or preventing thromboembolic disorders.
