Therapeutically active compounds of formula (I): wherein X is -O-, -CH2- or -C(O)-; Z is -CHR9- or valence bond; Y is -CH2-, -C(O)-, CH(OR10)-, -CH(NR11R12 )-, -O-, -S-, -S(O)- or -S(O2)-, provided that in case Z is a valence bond, Y is not C(O); the dashed line represents an optional double bond in which case Z is -CR9- and Y is -CH-, C(OR10)- or -C(NR11R12 )-; R1 is -(CH2)nNR4R7 or one of the following groups:n is 1 - 4; R2 and R3 are independently H, lower alkyl, lower alkoxy, -NO2, halogen, -CF3, -OH, -NHR8 or -COOH; R4 and R7 are independently H, lower alkyl or lower hydroxyalkyl; R5 is H, lower alkoxy, -CF3, -NH2 or -CN; R6 is -NO2 , -NR14R19, -CF3 or R8 and R16 are independently H or acyl; R9 is H or lower alkyl; R10 is H, alkylsulfonyl or acyl; R11 and R12 are independently H, lower alkyl or acyl; R13 and R18 are independently H or -OR20; R14 and R19 are independently H, acyl, alkylsulfonyl, C(S)NHR17 or C(O)NHR17; R15 is H or NH2; R17 is H or lower alkyl; R20 is H or acyl; and pharmaceutically acceptable salts and esters thereof are disclosed. The compounds are potent inhibitors of Na+/Ca2+ exchange mechanism.