Guanidine derivatives having a condensed tricyclic ring of formula 1: are disclosed, wherein U is C(O), CRaRb, O, NRa or S(O)m; V is CRaRb or NRa; W is S(O)m; wherein Ra is H, alkyl, cycloalkyl, alkenyl or aralkyl; Rb is H, alkyl, OH, ORa or OCORa, and m is the integer 0, 1 or 2; R1, R2, R3, R4, R5, R6, R7 and R8 are as defined herein with the proviso that at least one of R1, R2, R3, R4, R5, R6, R7 or R8 is guanidino or guanidino carbonyl. These derivatives are sodium-proton exchange inhibitors and are useful as medicaments for the treatment of, for example, organ disorders associated with ischemia and reperfusion, cardiac arrhythmia, cardiac hypertrophy, hypertension, cell proliferative disorders and diabetes.