A compound having structural Formula I or a pharmaceutically acceptable salt thereof wherein: Z is X 1, X 2 and X 3 are each independently selected from C(R 4) or N; one of X 4 and X 5 is *-C and the other is C(R 4) or N; provided that at least one and at most two of X 1, X 2, X3, X 4 and X 5 is N; Each R 4 is independently -H, halo (particularly -F or -Cl), -CN, -C 3-6 cycloalkyl, -C OC 1-4 alkyl, -OC 1-4 alkyl, or -C 1-4 alkyl optionally substituted with -OH or 1-3 of-F; wherein * indicates the point of attachment to the N-tetrazolyl ring and ** indicates the point of attachment to -CH -; R 1 is -H, halo particularly -F, -OH, or -OC 1-3 alkyl particularly -OCH 3; m is an integer selected from zero (R3b is absent) and 1 (R3b is present); R 2 is -H, =O (oxo), -OH, -C 1-3 alkyl or -OC 1-3 alkyl; R3a is -H,-C 3-4 cycloalkyl or -C 1-3 alkyl optionally substituted with -OCH 3 or 1 to 3 of-F; R3b is -H or -C 1-3 alkyl, or R3b is absent when the dashed bond is a double bond; or R 3a and R 3b are joined together with the carbon to which they are both attached to form cyclopropyl or cyclobutyl; R5 is -H, halo, -C 3-6 cycloalkyl or -C 1-3 alkyl optionally substituted with -O-C 1- alkyl; R6 is -H or -C 1-3 alkyl; R7 is -H or -C 1-3 alkyl optionally substituted with -OH, -OCH 3 or 1 to 3 of-F; R8 is -H or -C 1-3 alkyl; or R 7 and R 8 are joined together with the carbon to which they are both attached to form -C 3-4 cycloalkyl; R9 is -H, -F, -OH, -C 1-3 alkyl, -OC 1-3 alkyl or -CH 2 OH; R 10 is -H, -C 1-3 alkyl optionally substituted with -OH, -OCH 3, or 1 to 3 of-F; R 11 is -H, -C 1-3 alkyl optionally substituted with -OH, -OCH 3, or 1 to 3 of-F; or R 10 and R 11 are joined together to represent -CH 2 -CH 2 -, -CH 2 -N(CH 3)-CH 2 - or -CH 2 OCH 2 -; R 12 and R 13 are each independently -H, halo (particularly -F or -Cl), -CN, -C 3-6 cycloalkyl, -C OC 1-4 alkyl, -OC 1-4 alkyl, or -C 1-4 alkyl optionally substituted with or -OH or 1-3 of -F; and the dashed bond ("- - -") represents a single or double bond provided that: (i) when m is 1, then the dashed bond is a single bond; and (ii) when m is zero and R 2 is not =O, then the dashed bond is a double bond. Z is X 1, X 2 and X 3 are each independently selected from C(R 4) or N; one of X 4 and X 5 is *-C and the other is C(R 4) or N; provided that at least one and at most two of X 1, X 2, X3, X 4 and X 5 is N; Each R 4 is independently -H, halo (particularly -F or -Cl), -CN, -C 3-6 cycloalkyl, -C OC 1-4 alkyl, -OC 1-4 alkyl, or -C 1-4 alkyl optionally substituted with -OH or 1-3 of-F; wherein * indicates the point of attachment to the N-tetrazolyl ring and ** indicates the point of attachment to -CH -; R 1 is -H, halo particularly -F, -OH, or -OC 1-3 alkyl particularly -OCH 3; m is an integer selected from zero (R3b is absent) and 1 (R3b is present); R 2 is -H, =O (oxo), -OH, -C 1-3 alkyl or -OC 1-3 alkyl; R3a is -H,-C 3-4 cycloalkyl or -C 1-3 alkyl optionally substituted with -OCH 3 or 1 to 3 of-F; R3b is -H or -C 1-3 alkyl, or R3b is absent when the dashed bond is a double bond; or R 3a and R 3b are joined together with the carbon to which they are both attached to form cyclopropyl or cyclobutyl; R5 is -H, halo, -C 3-6 cycloalkyl or -C 1-3 alkyl optionally substituted with -O-C 1- alkyl; R6 is -H or -C 1-3 alkyl; R7 is -H or -C 1-3 alkyl optionally substituted with -OH, -OCH 3 or 1 to 3 of-F; R8 is -H or -C 1-3 alkyl; or R 7 and R 8 are joined together with the carbon to which they are both attached to form -C 3-4 cycloalkyl; R9 is -H, -F, -OH, -C 1-3 alkyl, -OC 1-3 alkyl or -CH 2 OH; R 10 is -H, -C 1-3 alkyl optionally substituted with -OH, -OCH 3, or 1 to 3 of-F; R 11 is -H, -C 1-3 alkyl optionally substituted with -OH, -OCH 3, or 1 to 3 of-F; or R 10 and R 11 are joined together to represent -CH 2 -CH 2 -, -CH 2 -N(CH 3)-CH 2 - or -CH 2 OCH 2 -; R 12 and R 13 are each independently -H, halo (particularly -F or -Cl), -CN, -C 3-6 cycloalkyl, -C OC 1-4 alkyl, -OC 1-4 alkyl, or -C 1-4 alkyl optionally substituted with or -OH or 1-3 of -F; and the dashed bond ("- - -") represents a single or double bond provided that: (i) when m is 1, then the dashed bond is a single bond; and (ii) when m is zero and R 2 is not =O, then the dashed bond is a double bond. (i) when m is 1, then the dashed bond is a single bond; and (ii) when m is zero and R 2 is not =O, then the dashed bond is a double bond.