N-Heterocyclic derivatives of the following formula: where m, n, p, A1, R1, R2, R3 and R4 are described herein, as well as other N-heterocyclic derivatives, are useful as inhibitors of nitric oxide synthase. Pharmaceutical compositions containing these compounds, methods of using these compounds as inhibitors of nitric oxide synthase and processes for synthesizing these compounds are also described herein.