The invention relates to a fungicidally active compound of formula (I): where Het is a 5- or 6-membered heterocyclic ring containing one to three heteroatoms, each independently selected from oxygen, nitrogen and sulphur, the ring being substituted by the groups R6, R7 and R8; R1 is hydrogen, C1-4 alkyl, C1-4 haloalkyl, C1-4 alkoxy, C1-4 haloalkoxy, CH2 C≡CR9, CH2 CR10═CHR11, CH═C═CH2 or COR12; R2 and R3 are each, independently, hydrogen, halo, C1-4 alkyl, C1-4 alkoxy, C1-4 haloalkyl or C1-4 haloalkoxy; R4 and R5 are each independently selected from halo, cyano and nitro; or one of R4 and R5 is hydrogen and the other is selected from halo, cyano and nitro; R6, R7 and R8 are each, independently, hydrogen, halo, cyano, nitro, C1-4 alkyl, C1-4 haloalkyl, C1-4 alkoxy(C1-4)alkyl, C1-4 haloalkoxy(C1-4)alkyl or C1-4 haloalkoxy, provided that at least one of R6, R7 and R8 is not hydrogen; R9, R10 and R11 are each, independently, hydrogen, halo, C1-4 alkyl, C1-4 haloalkyl or C1-4 alkoxy(C1-4)alkyl; and R12 is hydrogen, C1-6 alkyl, C1-6 haloalkyl, C1-4 alkoxy(C1-4)alkyl, C1-4 alkylthio(C1-4)-alkyl, C1-4 alkoxy or aryl; to the preparation of these compounds, to novel intermediates used in the preparation of these compounds, to agrochemical compositions which comprise at least one of the novel compounds as active ingredient, to the preparation of the compositions mentioned and to the use of the active ingredients or compositions in agriculture or horticulture for controlling or preventing infestation of plants by phytopathogenic microorganisms, preferably fungi.